Had a similar situation. Only one ball when pup was checked at our Vet. Breeder kept saying it would show up. It never did. Dog is 2.5 now and we had them remove both because most folks with quality females have quite a choice of which stud dogs they want to use, so his value in terms of breeding is nil unless I want to start my own breeding program, and it didn't seem like a good idea to do that with a dog where there is a question about the one ball thing...
The other side of the equation is that the purchaser of the pup paid full money for the pup who was found to have a basically disqualifying fault in terms of breeding. They pointed it our right away when they first got the pup. They were advised by the breeder to wait and see. I realize there can be ton's of disqualifying faults that you can't find until much later in life, but it does seem somewhat questionable to charge full price for a puppy that has an apparent fault right out of the gate. By the time you wait 8 months, you have tons of affection, time, and money in the pup...
In my case, we love the dog, and he's fantastic - sure wish he had 2 balls, but he's such a wonderful dog in ALL aspects other than the uniball issue I'd buy him all over again knowing the problem.
We did have them go in and remove it. I might have left the other because I think there's a value in the dog having the full hormonal complement on board, but we added a female pup to the household, and since the male is 2.5 and there shouldn't be developmental issues with not having his balls at this point, we took them both since we disqualified him as a stud candidate and it would be such a hassle to deal with an intact male and a female in heat in the same house.
It was a really hard decision for me, because he is such an outstanding and talented dog both at home and in the field, and loves to train etc. Based on that he'd be a great stud. However, in order to decide to stud him, I'd have had to have all of the other genetic tests - hips, elbows, eyes, EIC, CNM etc etc etc done. That costs money, and considering starting with a dog with what most experienced breeders would consider a disqualifying fault, it just didn't seem like a good investment.
I'd say for future reference, I'd check or ask before getting a male if there were two balls, and ask for a guarantee of some sort that there will be 2 balls etc. Not sure that's a standard guarantee, and realizing that they do sometimes drop quite a bit later it would have to be some kind of money back, or something if it didn't drop.