Advice on finding/interviewing a trainer

[Korch]

A bit of background: I'm 6'1" 250 mostly fat. I've been working consistently for about 6 months (lifting, boxing, and other cardio) 4-7 times/wk. For roughly 6 months before, I was doing less intense lifting/cardio (and lost ~100lb). I'm interested in getting involved in a good lifting routine, so I want to go with something of the rippetoe/star5x5 variety. I just bought Rippetoe's Beginning Strength and will read that. From what I gather, both guys recommend compound exercises (squats, deadlifts, etc.) and, frankly, i don't know how to do them and I don't want to hurt myself. I've tried to read descriptions online, but it's tough.

So I'm looking for a trainer to help make sure my form is good, and eventually I'll go it alone. There's a nice gym nearby that I'll probably join (the gyms i currently have access to won't really fill my needs). I'd like to use one of their trainers but I've heard horror stories of ignorant trainers on here so I was wondering if any of you can offer me advice on weeding out the bad ones and finding the good ones. Should I pick the gym, then the trainer or vice versa? Thanks in advance.