I never been scammed because I simply do not trade or buy things from people that are not having a good feedback or not even have one these days its just so important to be on the look out.
Even if the trader is having a positive feedback, there is no guarantee that he will not try to con you. For example, in SR 2.0, there were some vendor accounts which had very good feedback, and still cheating their clients. I don't know what happened. Perhaps some scammer hacked these vendor accounts, and then used them to rob others.