Based on the amount I will pay up to 90% face value, but I need proof of being legit cards / e-cards. I would rather pay more and be safe than otherwise. Also I'm interested in an ongoing business for buying Amazon gcs.
What proof would satisfy you? There no real way to tell wether these have been carded somewhere down the line. If you do buy these you should know the risks, but if you buy one create a new amazon account and spend them as fast as possible so you don't get burnt.
There are multiple ways in which someone can prove that their merchandise is legitimate. A very simple example that will get you 90% face value from me would be a cash receipt that matches your gc's unique # (not claim code). Again, I will pay one of the highest rates but that comes with strings attached, and if your stuff is legitimate why shouldn't you go for the highest price? For lower quality, depending of potential risks I will pay less, but still above the typical 70% (or less) face value around here.