I no longer do any fsg cleans, or gutter clears, on houses; my shoulders aren't up to it, so I have to be careful.
However, I am happy to do bungalows.
Any work I get, (and I do get quite a bit) I give to my mates (fellow window cleaners) one also specialises in fsg and gutter clearing, the other does roof cleaning as well.
I don't charge a percentage, I just give it to them for free. They make sure my customer is looked after and every now and again, they take me out for a slap up meal...and drinks...and taxi!
If I were going to charge, then perhaps 10% - 15% finders fee sounds reasonable. I wouldn't charge though, we just all do each other favours.
As long as my customers are looked after properly, i'm happy. That's my concern.