1. Amazon has a HUGE scamming problem right now. Fraudulent listed items are a big deal, combined with legitimate listings, so it's hard not to get suddenly overcharged or sold a cheap knockoff. Your credit card number might be safer, but your actual money probably isn't.

2. You're not responsible for fraudulent charges, so worrying about major retailers having your credit card number isn't really reasonable. I don't recommend saving your credit card in any store website. Enter it each time so they can't store it.