I am under the impression that you are buying the fiverr gig and not expecting to receive the actual gig in return, is that accurate?
You may have better luck if you offer to send $5 via paypal to any person who will give you three likes on DP. Therefore you are paying the same amount, but getting vastly more people interested (as not everyone sells via fiverr, but about 100% of internet marketers have a paypal account). Also, fiverr sellers are only receiving $4 for a sale (and I assume most people would rather receive $5 than $4). While I understand where you're coming from with the whole "you scratch my back, I'll scratch yours", if your main goal is to get likes, just send $5 via paypal to any person who gives you three likes on DP.