It's best not to say "avoid vets"...a veterinary surgeon and the owner are the only people legally allowed to treat animals, and there are laws governing that if an animal is in need of medical attention, you must allow them it. You cannot deny the animal the medical attention if a vet is the only option. If there is a local rodentologist available, then it's advised to go to them, but not everyone is able to travel and seek the specialist care for their pigs. Sometimes, working with a semi-decent vet is the only thing you can do.
There are some very bad vets out there, and yes you'd be better off avoiding them altogether - but if your only vet is a bad one, then surely it is better to advise the owner of what to ask for, what not to allow to happen, encourage the owner to protect the pigs by working with the vet, rather than suggesting going straight against what may be their only source of medical support? Not every vet is bad - Vedra works with vets and she has trained vets to become rodentologists also. Alastair and Amir are two that come to mind who she very highly recommends, and she will advise of suitable vets that she knows of.
It's more a case of "find the best you can". Find a rodentologist; if not then find the highest recommended vet you can get to, and if necessary take along the information you need to back up what you think or know.