I would ask:
Who is your insurer?
What is your accident policy?
How will you deal with my dog if they react to pain or discomfort by growling or snapping?
How will you keep my dog safe during their groom?
What specifically is their safety policy on dryers?
If they can't give satisfactory answers to those questions, if they act shirty or pissed off that you've asked them or if the answers seem like bullshit - run the other way.
Things to look for:
Clean shop.
Not too noisey - some dogs will bark but it shouldn't sound like LOADS of dogs having a massive bark fest. If it is, that suggests they are taking on too many dogs and rushing them as a result.
Tables should be clean, non-slip, have an H bar or L bar with restraints, and various sizes of restraint according to the dogs size.
They should have disinfectant and multiple clipper blades/scissors they can disinfect between clips.
If you can't come back and see this, (you may have to arrange a suitable time to see their set up of course, its not appropriate to have a member of the public just wander in during the middle of a working day!) then again, I'd be concerned.
Avoid anyone who uses box dryers - effectively a big heated box your dog is shut in - crates with dryers pointed at them are safer but still... find out if dogs are left in crates with warm dryers pointed at them in another room, as dogs CAN be forgotten and overheated this way!!
The very best thing you can do though is teach your dog from day 1 to think standing on a grooming table or vets table and having someone touch them all over, lift paws, look in eyes and ears and mouth etc and brush/comb etc, is a GOOD thing. I don't mean 'tolerate it' I mean actively think its a nice thing.
If every owner did this, far far fewer dogs would be manhandled and frightened at the groomers and the vets.