In the original scenario - Zero, notta, zilch.
With risk comes reward, the marble contractor has no risk.
Scenario A: The marble contractor tells me he can get a job for me. My contract is with the homeowner. He wants a percentage for the referral. ZERO.
Scenario B: The marble contractor tells me that he can get a job for me. My contract is with the marble contractor. His contractor is with the homeowner and includes the scope of my work. He marks up my price by 20% and that price is in his contractor with the homeowner. Good for him, I don't care what he makes on my work. If for some reason there is an issue with my work the homeowner has to go to the marble contractor and he has to come to me. If i fail to perform he has the risk and will have to perform. He has risk so he should be rewarded.
Scenario C: The marble contractor get a 20% finders fee from me. My contract is with the homeowner. The marble contractor damages my cabinets and hard feelings develop. In the end to get even with the marble contractor I tell the homeowner that in the future I can give better pricing because I will not be paying a finders fee. OOPS for the marble contractor.
Scenario D: Contractors who have paid the fee end up doing lousy jobs and somehow it makes it to the internet and two and two is put together. The verdict - the marble contractor doesn't care about his customers and will sell influence in order to make a buck. OOPS. OOPS
Don't pay it.
Peter