Even though I will buy a house using my realtor, I always felt bit bad for him showing us all the houses that we will NOT buy. He doesn’t have the certainty that we WILL buy a house at all, or stay with him. I think realtors should be paid for those hours too, I mean before you buy also. That will reduce the number of flakes and looky-loos, too, I am sure.
Perhaps a better would be a initial flat rate covering X hours, and then hourly based fee after that. And then, if you close a deal deduct those fees or a part of them (like a deposit) from the commission.