What Happens When A Gift Card Is invalid?

[CrackedLogic]

I trade a lot with gift cards - inside and outside of bitcoin - It has never crossed my mind until now;

What happens if I buy an eGift Card ( or any gift card for that matter) and it turns out that the gift card is invalid?
Proving this can be horrible as there are 1337 h4xxors that are able to use "inspect element" and/or change the pages' source and take screenshots and send it to the escrow/seller and "prove" that it doesn't work.

Other than contacting the Retailer/service provider and asking them for when the card was redeemed, what else could you do?
Some retailers don't even have gift card verifying methods(primarily local small stores).