This is a very solid warning bro!! a lot of people think because they know someone on a personal note, so that automatically makes the deal safe but in reality, trust does not protect you if the Bitcoin or any other coin at all turns out to be a stolen one.
You're very correct, no matter the relationship we don't have to trust anyone completely because you may be thinking that they can't harm you or do something bad to you but you will be surprise to see the other side of them some day. if it was before that was during the early stage, face to face exchange is the most recommendable method while few was trading with online P2P and then things wasn't that bad as it was in this current stage, is obvious that alot of things has changed and the rate of envy is very high which is why we have to adopt the new method of exchange so that to enable us be in the safer side even though online P2P is not risk free but I think it is more preferable than face to face exchange.