If you've never heard of this site, https://rep.tf will inform you, using just their Steam ID
(also known as their Steam Page URL), their history in relation to various sites.

In the event the account is banned from either a major trading website or Steam itself, it will give a large red warning saying the following:
Notice: This user is banned from one or more communities. These bans may not be trade related. You should use this information to determine if this user is reputable.

it's a good sign you may want to reconsider adding them.
If they are banned from Backpack.tf, see the reason why their account is banned.

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Simple check - if they claim to be a trader, check if they have a Public Backpack.
Right below the games button on their Steam Profile, there should be a button labeled Inventory. If you're met with the following message:
User's inventory is currently private

that's a huge warning of who they may be.
While there are some traders which may be legitimate that happen to have a private inventory, you should be concerned.
If you do add them, and their inventory does show up - then you shouldn't be concerned.
But if it's still private, that's when you should reconsider.

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Bit of a more obscure thing to check - but if an account has publicly available achievements for Team Fortress 2 - click the Achievement Progress text.

If the Records + Stats show up as blank for all classes, especially with hundreds if not thousands of hours, in 99% of situations, consider this as a sign they did not play, and instead farmed hours.
While there are some that will naturally delete their hours for many different reasons, this can be a clear sign of a Scammer - especially if they're ingame at the time of a friend request.

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If you didn't already know, Counter-Strike 2 only has one achievement.
Said achievement is rewarded for simply logging into the videogame.
If for whatever reason an account has thousands of hours in CS2 without this achievement,
most likely this is a suspicious account.

It is technically possible that said account could have used the Beta option in Steam to exclusively play Counter Strike: Global Offensive, but the odds of that are very slim.

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If someone were to actually report and get you banned from Trading,
the application itself will send a notification through Steam itself.
No employee or account will ever tell you of a report by adding you on Steam.

If you are genuinely paranoid about a report, and want to see what the actual message looks like, see the following Steam Guide:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=961168214

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If a newly added person needs your items for whatever reason without anything to compensate, it's most likely a scam.

If a newly added person wants you to send items to a bot or trusted account for whatever reason, it's likely a scam.

If a trade involves both parties sending your items to a middle-man, expect it to be a scam.
You don't need a 3rd Party to have the opportunity to just run away with the items

Traders very rarely have alternative accounts.
If who you're trading with links to an entirely different backpack, that's an impersonator.

This is a very context sensitive type of scam, but if it involves:

• Going to a competitive/tourney site
  
• Advertising a website
  
• Gambling
  
• Upvoting a Steam Workshop Item

it's most certainly a scam.

Be very mindful of the Steam URL if you do decide to log into a new website.
If it's misspelled or otherwise not steamcommunity at all, it's a definitive sign of a scam.

Note that if it was a real Steam Link, it should take you to the page inside of the Steam Launcher.
Anything else would redirect you to a third party website.

Even if the link itself is real however, there's a good chance that if they want you to go to a uncommon third party website, it's going to do some sketchy things, such as a roulette wheel with faked odds, that will inevitably steal your items.

Addition as of 1/20/2025
Some official Steam Logins - with simply having your Steam API Key - can abuse commit malicious acts, such as unwarranted one sided trades - and effectively hijack your inventory.
Some projects - such as Particle Mayhem, have been impersonated, so research before logging in.

This mainly occurs when making trades involving external items. (Gifts, Money, etc.)
Even after someone sends the money or games or whatnot, most offer a chargeback function.
Main catch - depending on the situation, you can get punished for their chargeback.

So when making trades that involve external factors, be mindful of who you're trading with.

You won't see this too often, but if you are a content creator, be mindful when accepting trades.
There's a non-zero chance someone will instead trade for your items in exchange for nothing.

A festive Weapon is a group of weapons that were only unboxable during Smissmas 2011, 2013, and 2014 in the Naughty/Nice cases of their respective years.
A festivized weapon in comparison can be created using a Festivizer, available in any Smissmas Case 2015 and onwards year-round.

Due to Festive weapons nowadays being limited in supply with generally preferred asthetics, they are considered much more expensive in trading than Festivized weapons.

As an example - the Festive Knife[backpack.tf] is valued over 10 Keys, while a Festivized Knife[backpack.tf] is valued at 1-2 Keys max.

Frequently, sharks will attempt to pass off Festivized Weapons as Festive, in the worst case resulting in the end-user swapping their Several Keys Worth Unusual for a 1-2 Key Festivized Weapon.

When trading for Festive/Festivized Weapons, pay attention for the yellow text - Festivized.
If a trade involves a Festive Weapon, but they trade over a Festivized Weapon, they're sharking.

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Addition as of 1/6/2025
Similar situation to Festivized vs Festive, but even more subtle.

Some items in TF2 happen to be way more valuable when they're one way or the other.

A common item that is abused in this way is the Lucky 42. While the Crafted version (which only about 100 of them exist) is worth around 30 Keys to traders - when Uncraftable (which over 3000 exists), it's worth closer to about 6 Keys.

Note that these numbers will change, but to give a rough idea on the difference.
Point being - make sure you're getting a good offer when seeing specific items.

This isn't that common anymore, but yes, there are people that do try to rename their items to convince people it's something that it isn't.
Most commonly, this will happen with Unusuals & Spelled Items on the Steam Community Market.

If you notice some Unusual is suddenly Yellow, or a spelled item's notation doesn't have special Blue Text, that's a sign something is wrong.

Before finalizing the trade, make sure the items you're receiving are what you requested.
Even if the item is an Unusual Team Captain, make sure it's Burning Flames and not Bubbling.

Addition as of 8/22/2024[scrap.tf]
While very unlikely to happen under most circumstances - some sharks have enough power to make several accounts appear as if they're going to buy an unusual for much higher than expected - but then immediately delist their offering (or otherwise not have the amount to even buy the item.) If you are going to trade for Unusuals - make sure the item is wanting to be purchased by legitimate, trusted traders.

While this type of scamming method seemingly isn't around anymore,
you should be aware of it anyways.

In short, some games in the past have been created to generate fake versions of legitimate items.
These items will appear as if they are real items, but in reality come from unrelated titles.

While Valve has gone out of their way to stop this scam, it can always come back.

For all that is good, don't feel rushed to trade away your valuables.
I know it's tempting to buy something new, but what you have now is fine enough.

More importantly, trade when you're awake.
Don't trade with 3 AM energy, as you're more vulnerable than ever to make stupid decisions.

The main goal of a trader above all else is trying to make a deal that will give them the edge.
Ultimately, if you believe the trade you're being offered is not worth it, then don't do it.

A trader trying to make a trade is not on its own a scam or a shark, but rather the context of it.
If it's so extreme that it has to been seen as a scam, then go report it only then.
But if it's just a bad deal, then move on with your life.

Self-explanatory. If you're making a trade and it sounds like something's off, that's likely the case.

I know it's funny to try it, but frankly, depending on who you're dealing with, it's a waste.
Some are automated accounts, so you're just making them run a macro a few more times.

For the ones that are real, you're only really going to stall them for some negligible time.
Some scam as a side-job, so frankly it's not going to be worth it in the long run.

When you can, report them on all fronts.
While it might take time, I've gotten at least one scammer banned on record before.
It might not be much in the grand scheme of things, to have action happen is nice.

Thanks for reading - stay safe out there.

Icon made using loadout.tf