Dont ever transact with strangers if you are not using escrow. Mostly scammers are hiding in a pretty girl profile pic or pretending to be a trusted by copying others reputable name.
If you're buying or selling cryptos either use a well known exchange or do it in person and take some people with you, don't go alone. Also, if you want a personal transaction, don't invite people to your home. You don't want them to know where they can find more money
If you're trading goods use escrow, it all comes down to this one simple thing.