How to buy Amazon coupons?

People sell their amazon.com coupons on ebay and other websites. In addition to possible fraud, I wonder how to safely buy an amazon coupon, as it is against the amazon terms.Imagine that I have bought a coupon on ebay, and redeemed it successfully in my account. Is it final? Can't the original owner claim that this is a stolen coupon? And doesn't amazon void a coupon?The reason that I am asking is that a coupon is issued to someone else (not me), and since buying/selling coupons are not allowed, Amazon may (I do not know, I am asking) void my coupon, as I was not the original owner?Is the owner of an amazon coupon is the one who first redeemed it? Or someone can claim?

I'd like to buy Amazon coupons too and if anyone has answers to the above question, I'd appreciate it.

I have a 900$ amazon card if anyone interested

check this read, mate: http://websearch.about.com/od/onlineshoppingsearch/ht/amazon-coupons.htm

Be careful coupons and tickets are not covered by buyer protection from ebay or paypal.