Abuse of online discount vouchers

[AlCapacino]

So there was a play.com one recently so for the first 8000 applicants, they would get £5 and then other would get £1 thereafter.

So on ebay and forums people are boasting how they got "loads" so it makes me wonder is there nothing to keep fairness/avoid abuse in the system?

[kickstart 1]

Your always going to get people who abuse the system and spoil it for others,but dont see how it can be stopped ,unless people given vouchers directly, or possibly given a code when they have actually bought something,so as to claim vouchers in the future.