They have Earn Bitcoin option on this site.
I want to know how it works.
They have earning calculator on this site.
According to my calculation :-
If I purchase $100 of gift card from amazon, then
I have to sell in $75 to them.
Where is the earning?
It's not really you'll use that option to earn bitcoin in a daily basis. This is like an incentive that you can earn from your gift cards that you don't mind using anymore.
Instead of not using them, you have an option to sell it to them in exchange of bitcoin.
I didn't heard of them until you introduced it.