If you don't want to do it but find it difficult saying no, tell him your dog has breeding restrictions on it as do all the other pups in that litter applied by their breeder and so he can't be used.
Good thinking Karen

My neighbour approached me the once to ask me about this, she was feeling very pressured by a friend who wanted to use her boy dog at stud 'because he had nice markings' (not knowing anything about his temperament, health status etc).

She stood her ground and said no about using him, especially as she has young children and didn't want his temperament to change. (Not to mention there being soooo many of that particular breed in rescue centres etc).