When I attended repair school in NJ, one of my teachers told me that there is one specific phrase that reveals whether a tech is a hack or a pro...
"This is how I like my guitars"
If you hear a tech or luthier say this, run away! Every single guitarist has their own style, attack, and technique. There are averages and common preferences, but 'common' doesn't mean 'universal.' What one guitarist likes, the other might hate.
I knew a tech who set up guitars so that they suited his style perfectly, but when he set up guitars for his customers in the same way, they complained about it being uncomfortable. He argued with the customers, saying "well this is how I like my guitar and I think it's the best way." I cringed whenever I heard that.
"I'm right and you're wrong"
If you ever bring your guitar to a tech and ask him or her to do part of a job in a very specific way, and they won't do it because they don't think it's "right," walk away.
For example, I recently had a customer who told me that he had been to three other techs before me who had all refused to do what he asked. Specifically, they refused to bring up the string action, or height, at the nut—something that is addressed during any good routine setup. The other techs told him that what he really needed was a proper setup or that high nut action is "wrong."
The request is so simple. A shim for one of the customer's guitars and some slot filling for the other. It didn't take more than 30 minutes and he was very grateful that I did the simple deed of doing what he asked.
I gained a loyal customer that day just by practicing good customer service, while those other techs lost one just so that they could preserve their egos.
So to sum it up: your guitar is an extension of yourself, and if a tech won't treat it as such, it's time to move on...to me, hopefully.