I have never seen a livestock veterinarian vent sex a chick let alone a half grown chicken, it's simply not something they are taught and if something were to go wrong they and their practice would be held liable (sister is a farm vet). I'm sorry but I'm skeptical or at least wouldn't be taking in all the information as anything more than simply a guess.
You're probably right about livestock vets, but there's at least one bird vet in Australia with a chicken specialist. It doesn't separate out the services offered by this individual, but they do offer sexing there: https://birdvetmelbourne.com/chicken-vet/
Don't know if this is who they went to, just pointing out that it's possible they have a vet that offers such a service.
Agreed. They can attempt it and get their money, but it's not like they're experts.Although we do have avian vets that also specialize in chickens, the only form of sexing available at any clinic is DNA testing via a blood or feather sample as vent sexing is a technique that is not taught.