There is no magic converting traffic source, any traffic source can be profitable, you just need to learn the traffic it sends out. You can gather data from the traffic source with your tracker, combine this data with the data that you get from running split tests and you should start to get an idea of what will convert against that traffic and what's going to be better promoted somewhere else. Different traffic sources will convert differently for different offers.
I think that buying coupons on Fiverr can be a wrong idea, since it can get your Bing account banned.
