First time using a stud dog – what should I ask the owner?

I know a few of us here will be using a stud for the first time, so thought it would be useful to have a thread on this.

What questions do you always ask a stud owner before agreeing to a mating? Things like health testing history, temperament, previous litters, and how they structure the stud fee versus a pick-of-litter arrangement all come to mind, but I am sure there is plenty I have not thought of.

Would be great to hear from more experienced breeders on what they wish they had asked the first time round.