Here are all of the scams that I know and that have been tried against me and how to avoid them! Good Luck!

•Give items to a friend scam:
A user will approach you and ask you to send your items to a friend before a trade. He will want to know the name of your friend. Once you send your friend the items he will make a profile identical to yours and ask your friend for the items back. Or he will change into your friends profile and get you to send the items to him first instead. To avoid this scam if someone mentions the involvement of a friend, block and report them.

•Give items to an admin or middleman scam:
A user will approach you and say that he will only trade if you both send your items to a 'legit' middleman or admin first. He will send you proof that this middleman is a real staff (of course this proof is fake). They will take your items and run off. To avoid this scam, wait until they mention the name of the middleman and then report and block both of them.

•Faulty or Duped items scam:
A user will approach you and claim that your items are faulty or duped and show you proof on CSGO-Exchange. He will then ask you to send the skins to him or a trusted admin (like above) to get them fixed. He will then run off. To avoid this scam remember that steam won't ban you for owning duped items, only if you did it yourself. Next, again, block both users and report them.

•Instant Counter Offer scam:
A user will approach you and will say that he has done plenty of trades and he buys skins off of a third party store. His profile will most likely be private. For a various reason he will ask you to send him a trade without the item you want in it and he will say that he will automatically counter offer with your item so that you can accept it. Instead when you offer him the trade, he will just accept it and leave with your items. If someone approaches you with this, report them.

•'I'm a steam(rep) staff' scam:
They will get you to send your items to them first so that they can check them. Then they just run off. If someone claims to be an admin and it does not say so on their profile, report and block them.

•Gambling site admin scam:
A user will approach you and link you a gambling site. They show you that they can rig it. You add skins to it and then realise that you can't withdraw stuff and all the players are bots. To avoid this scam do not log in to external sites and do not deposit items to them. Report them and their site, and block them.

•Gambling site scam:
Same as the above except when you put your items in and enter, you lose the pot to the owner of the site.... To avoid this scam do the same as the above.

•Phising site scam:
A malicious link that leads to a malicious site. Don't click links. To avoid this scam do not click links that are sent to you by other users.

•Virus/Key-logger download scam:
Someone wants you to enter their TS. You enter and a real looking update message pops up. You download it but with it comes the key logger. To avoid this scam do not enter Skype, TS or other sorts of communication softwares and do not download anything related to any lobby or server/channel that you join.

•Steam or Other card scam:
Someone will offer you these cards. Once you send them the skins they will run off. To avoid these scams do not accept steam and other cards as payment, ever.

•PayPal scam:
You will send the skins first and they will just run off or they will send you PayPal money and just charge back later. To avoid this scam, never accept PayPal or Bitcoin as a form of payment.

•'I go first' scam:
They will send you a horrible skin first or pretend to have lost a skin to you and then report you and complain about you everywhere potentially getting you banned or until you give them a skin. To avoid this scam just block, report and ignore them. If you have not broken any rules you will not be banned.

•'you go first' scam:
You send them your skins and they just leave. To avoid this scam only accept trade offers and do not accept live trades or go first.

•Item wear switch scam:
You see a skin you want in the FN condition and you send someone a trade offer. They counter offer with what seems to be the same thing but the wear is now WW. To avoid this scam never accept live trades and read each item very carefully before accepting a trade on your main device and authenticator.

•Threats and blackmail scam:
Blackmails you and threatens you with stuff like a ban until you send them your skins. If someone used any threat against you instantly block and report them.

•Live trade scam:
Apparently there's a way to spoof skins into a live trade but I'm not sure if this is true. But live trades aren't very good. Avoid them for many reasons. To avoid this scam never accept live trades.

•"Hidden item(s)" scam:
You will receive a trade offer for a Karambit for all of your junk skins and you will accept it right away, not realising your dragon lore was hidden in the centre. To avoid this scam carefully and slowly view items in a trade before you accept a trade on your main device and authenticator.

•'Storage' scam:
Users pretend to have skins on a different account, but that account is not theirs at all. They then try various scam attempts until you get scammed. The other account that they linked belongs to someone else but they copied their profile to look similar to it. To avoid this scam do not trust users with a storage in their profile or with a private inventory. Or who claim they have the items on a different account.

•Gambling or store bot scam:
People will record your stream and buy or win skins from something. They will see what you won and If you already have some of those skins they will mimic a trade not but instead of giving you items, they will request them from you. To avoid this scam carefully view and accept trades across your devices.

•Fake YouTuber scam:
someone will go to you with a profile that looks identical to that of a youtubers. They will ask you to give them skins for a video and they will pay you some money. Simply block them and report.

•Fake item price scam:
A user will approach you and say that he has a friend who will buy your knife for a super rare and expensive Dota2 or other game item. He will give you a super bad worthless item that has been manipulated in price to seem higher in the market by scammers. After the trade he will have your skin and you will have a worthless item. {This exact scam was told to me by Lemonhead21Mascot who also gave me permission to post it here}

•Other paypal scam:
A user will send you a paypal invoice saying that you have either scammed him and he will 'sue' or something if you do not pay it. Or he will come to you to trade and instead of sending you paypal money he will try taking it from you, or he will try something similar. {This exact scam was told to me by Lemonhead21Mascot who also gave me permission to post it here}

Basically the simplest ways to not get scammed is to only accept normal trade offers. Never to click links or send items first to anyone. Block people for reasons listed above and to be very careful when accepting trades. Also do not accept anything other than market currency (no paypal, bitcoin, steam cards, etc). Do not get involved with other sites or log into them. Do not gamble on untrusted sites. Basically do not do anything that can lead to any of the above. If someone tried to scam you, give them -rep on their profile and report them for 'attempted trade scam' and anything else they tried to do. Report their friends and assistants who tried scamming you also.

Good Luck! Have Fun! Keep your items safe!

[Special thanks to Lemonhead21Mascot for helping with typos and contributing to two paragraphs]