I got a ad for Benchmade knives. The knife I looked at was 80% off. Big tip off it can't be real. Looks very legit especially since they take major credit cards.
Remember what Abe Lincoln said, “not every thing on the internet is true.” I read it on the internet so it had to be true and honest Abe would never lie.
If the deals sound too good to be true... If the payment method is direct transfer or crypto-currency instead of credit card... If the supply of hard or impossible to find items is really good... odds are it's a scam and you will have no recourse.