If you are into the making money online game - for example through writing, then the time will probably come that you have to many Amazon vouchers and want to offload some on E-bay.
You will see that there is quite a market for this as not everyone has a credit card. It's a dangerous game to play though.
If you are a seller beware that:
Hypothetical Situation #1 -The buyer makes the purchase, sends the money over. You send them the code. You check your paypal account a few hours later and the transaction is frozen because the buyer's account is expected to be fraudulent. They've used your code and you don't get the money.
Hypothetical Situation #2 - The buyer makes the purchase and sends the money over. You send them the code. The buyer makes a claim on paypal that he didn't get the item. In the past this was a common occurrence and you would get neither money or code. I believe that this is no longer possible and that's because of situation #3.
There are plenty of people there that see that buying a $100 Amazon voucher for $90 is good business but it's not always the case. If you are a buyer beware that:
Hypothetical Situation #3 - As a buyer you send them the money. You do not get your code. You contact E-bay or Paypal but they cannot help. They do not protect buyers of Vouchers.
This applies not only to Amazon vouchers but to all types of vouchers on E-bay.