I think that it's a good decision that you see a trainer, if you feel that you would like other opinions, and options with your workouts. There are so many routines, and resources available.
Things that I would look for in a trainer are:
1) Qualifications; Degrees, specialty training knowledge etc. (Not always necessary, but great for peace of mind, and insurance issues)
2) Personability. You are going to be spending a lot of time with this person. Make sure that you'll be able to handle it.
3) Physical fitness. If they can't keep themselves in shape....forget about it!
There are also things that you need to tell your trainer, in-order to help them out.
1) Be specific! Don't say, "I want to lose 20 lbs". Say, " I would like to gain muscle mass, and definition in these areas, while reducing the circumference of these areas...you get the idea.
2) Plan ahead! Find out what times you can meet with him/her. If he/she's always booked, or in school, then you might want to try someone else.
3) Introduce YOUR ideas, routines, and knowledge with him/her. Chances are that they will be more then happy to work with them. After all, the idea is to keep YOU interested.
4) You might even want to ask if they have any before/after shots of past clients. If not..no big deal, but if they do, it'll not give you an idea of their success, but it might help you Visualize your outcome.
Hope some of this helped.