I do the vast majority of my own work (I have my own shop, afterall) but when I need work done by someone else there are only three people (at three different shops) that I'll take it to. It's not that I don't trust random wrench (but if random wrench can do it, I can do it better), just that I've built relationships over the years with specific mechanics. They ride with me, know my bike, and know what kinds of questions to ask about problems.

My answer to OP: 1st, many shops see very little in the way of fixed-gear stuff, and the wrench who put that on may not have known what he/she was doing. Go back and tell them and they'll fix it up nice. 2nd, find a shop that sells the type of bikes you're into and spend your time/money there. Talk to folks (but don't waste their time if they're busy), get to know a few, see who rides what, etc. Take future problems to them.