That is a good question. But think about it, why would compliance be low? It's not like you have to wear a giant rubber dick on your head to advertise something. You only wear a t-shirt or put a bumper sticker on your car. Possibly, of a brand that you might actually like. Where exactly is the incentive to cheat? Sure, some people might cheat and there are ways in which you can minimize this number of people which we've been discussing. But for the majority, there's really no incentive whatsoever to not wear that t-shirt and not fulfill their obligations.
We are actively working on a multisig scheme where advertisers won't need to trust us with the money and we will only act as a pure middleman, signing transactions when the campaign is completed. The scheme is relatively well know at the present stage of Bitcoin development, but it still takes some time to implement right. We ourselves are not interested in holding other people's funds, it's dangerous.
Anyway, project's good. Will donate when I can. Someone do it now tho, this looks like something most of us can put to good use.