I'm suggesting Amazon can be trusted with my credit card, and implying I would use them over any other merchant as long as I am reasonably sure I am getting something genuine. Prime or Fulfilled By Amazon are pretty good determinations that I'm either getting something legit or I have a very clear path to return the item and get my money back.
I can't say the same thing for a billion other little shops online. If you can't trust that a product on Amazon is legit, how can you trust some no-name site? I can't see how "www.Totally-Legit-Nail-Gun-Depot.info" can be any more deserving of trust than the largest online retailer in the world who has a better-than-world-class return policy.
That's like saying "I've been burned by bad doctors in the past, I'm going to have my brain surgery performed by this guy in an alley". I don't care how many patient referrals Alley Guy has, or that I have life insurance in case he kills me.
Better the devil you know, right?