Legality of reselling coupons, gift certificates, etc

[depokerstar]

Subject - reselling coupons, gift cards, travel vouchers, gift certificates, etc through eBay or other channels.

Most, if not all, of these items seem to place the burden on the potential buyer or "redeemer" of the coupon/certificate. What are the potential legal issues with buying and re-selling?

I am not talking about trying to sell coupons out of your Sunday paper on eBay for $.99. I'm concerned with large transactions. Example - if one had the ability to buy Amazon gift certificats at $.50 for each $1.00 or a simlar percentage with American Airline miles, Chili's gift cards, etc, while buying $10,000 - $20,000 at a time. It would be easy to resell these and make a nice profit.

My issue is related to the legality around this. There would be some type of signed agreement, since usually these are used for promotional purposes, sales incentives, etc. If those weren't abided by would a likely scenario be just being cut-off from future purposes?