Hi Ade,
This can be risky at times!!! The customer that referred you could have a big house and your new customer a small house, so you would really be loosing out money wise, if that were how you operated it.
I offer my clients the following. 10% discount of their next window clean per referral that takes our service on. If they recommend 5 new customers they receive 50% discount and if they recommend 10 new customers, their next clean is then free.
This works really well for me, please I do not loose a stack of money in the process.
Andrew