
First, have a read of the first post on the Breeding forum of this site.
You'll need to check his registration papers (and the bitch's) to find out if either of them have endorsements. Both dog and bitch will need to have passed all the breed-relevant health checks for hereditary conditions (
not a quick once-over by the vet), which certainly involves hip scoring (done by x-ray and the plates scored by the KC/BVA panel) - there may be other tests. He'll also need to be a good example of his breed, so he'll need to be independently assessed (likewise the bitch) - maybe his breeder will be able to help there if you haven't shown him.
You'll also need to be prepared for possible changes in his character and behaviour after he's been used at stud, even if only once. He could become male-aggressive; he could start urine marking indoors.
The usual stud fee for an unproven dog is generally very low, with maybe an additional payment when puppies are born - but without evidence that he sires good quality puppies (successful in the showring) then don't expect to get much money from it - £200 for a gamble like this would be pretty good; after all, there are some very successful stud dogs out there that they could use - I wonder why they want to use a pet dog?