Pet shops are notorious for being wrong. They don’t know half the time, but the baby bunnies are so, so young when they come in, there’s little risk of pregnancy with everyone in the same tank.
You have to have an initial exam prior to any type of surgery. The vet will give him a thorough check-over, check weight, estimate his age, check ears, eyes, nose, teeth, temperature, and perform a fecal test to rule out parasites like coccidia (which is not uncommon in petstore/breeder bunnies). You can also ask a vet tech to demonstrate nail-trimming for you if you want. All of this info will clear him for surgery and you can hopefully schedule it ASAP.
Bring any questions you have to the vet, you can talk about his housing, his daily exercise time, diet, or any behavioral concerns you might have. Rabbit savvy vets are a fountain of knowledge! Do your research ahead of time and this can help you gauge the vet by comparing what they say to what the House Rabbit Society says. The vet should be relatively consistent with those guidelines.
Have you been looking for a rabbit vet in your area yet? HRS has a page with vets by state.