I think this depends entirely on your market. If homes are sweeping off the shelves, there's no reason to waste the money. If you're in a slower market, I've seen anywhere from $1,000 to an extra 1% generate interest.
I'm interested if others have had success with this, though, and I'm curious what people think of the ethics involved on the buyer's agent side.
I am an agent, as well as someone who flips. I do not expect bonuses nor offer them on my flipped properties. Almost no agents actually look at how much the fee is. We show the appropriate properties to the appropriate clients. There may be a few agents that are incentivized by this....but they are not the agents who do a lot of volume and thus not the agents who can bring you a lot of buyers.
On the buy side I don't even look at the cooperation fee until we have a property under contract.
I think it all depends on your market, value of property, etc...In a hot sellers market, the agents job will be a cakewalk and no bonus is needed. If opposite, then I would do it.