As far as scamming goes in Rocket League, there's not much room to do it. Still, there are ways and it HAS happened before, so the best way to watch out for them is to know how it can happen:

This is the most commonly used method. The scammer will make you want to trade with him by proposing an awesome deal for you. Normally these are trades that involve a lot of items, at least enough to fill his trade window, but it can be done with only a couple of items or even just a single one. The scammer will then distract you by either being annoying, constantly proposing other trades, cancelling the trade several times, etc. This is when he swaps his items for similar ones (not certified, or less valiable but similar looking items) , making the trade go the scammer's way while you lose all your value in the trade.

We don't accept these types of trades in the group, but if you do take part in any, do it with absolute caution. This is by far the easiest way to get big profit from a scam. The scammer can cancel the money transfer on PayPal, not trade with the CSGO items, etc., pratically leaving you with nothing in a few seconds. The best you can do is find an official, trusted middleman to hold the items and supervise the trade. And, obviously, avoid going first if you can.

(more to be added)