Depends on the terms of service whether they are legal.
Yeah, as it turns out, they are not very friendly with unauthorized sellers.
There are certain restrictions in connection with the use of Amazon.com Gift Cards. If you engage in these activities, Amazon.com may prevent you from claiming or redeeming gift cards, or may take further action on your account without a refund.
[...]
- Purchase a gift card from an unauthorized third party as we cannot guarantee that they are legitimate.
I've been buying iTunes cards regularly for some time and I've never had any problem redeeming them.
Was it Coinsbee or Bitrefill? These are probably authorized.
Well if they just show you a code, it could already have been redeemed so buying them by P2P is very risky.
When selling in DEX, the buyer sends you the gift card first, so you get to verify it redeems.