You don't really have to visit a shop before going there. What's key is getting experiences from existing and former customers. Get the bad and the good. Listen to the details. Some people are fanbois and you should be able to filter those people out.
Some people are extremely jaded, and while their negative experience should weigh in a little more, you have to also consider that people generally don't tell you both sides of the argument.
Also a lot of customers just get really simple shit done and go all bonkers.
"OMG this shop installed my exhaust and they're awesome!" LOL.