
This is a very odd situation. For starters -
What stud dog owner 'drops their dog off' with the bitch? Surely she'd want to be there to help her stud dog do his job, if not to see whether or not he did the job!
Secondly why pay for the Service, when he didn't do the job?
Thirdly just because he didn't mate with your bitch doesn't mean 'they are not suited'. She probably wasn't anywhere near ready - is the dog a proven stud?
If she wasn't THERE on any of the days she'd left her dog with you, how does she know what happened. It's your word against her's that no mating took place. Mmm difficult.
There's no way you should have allowed her not to be there with her dog for the mating but if you are telling the truth and her dog didn't mate with your bitch, then she has no right to the stud fee (in my view). So that being the case, if she refuses to make you a full refund (I'd not want a 'next season' repeat under these circumstances), take her to Small Claims Court.
In most cases, the bitch goes to the dog. In most cases if there's a mating, the stud fee is paid (unless by prior agreement only when there are more than 2 puppies on the ground, if the dog isn't a proven dog) at the time of the Service.
How do you know whether your bitch was on the right day(s) to be mated? Testing is good but so is the reaction of the experienced Stud dog and if he wasn't interested, she either wasn't ready, or had perhaps gone over.
You probably should start a new thread about this situation.