What advice would you give a customer looking to hire a provider in your area of work?
Ask for success stories with before an after photos. If they dont have any they either are new to the industry, not skilled enough to help, or not passionate enough. It's a bit of a double edge sword. What I mean is if you want a skilled professional you will have to pay some wheres in the neighborhood of $75 per hour but if you refuse to pay that then you can get a significantly less skilled professional for $40-60 per hour.
If you are looking for both skill and affordability you may find a few trainers who offer both group and personal training. For example I offer both services and have pre-arranged groups that newcomers are encouraged to join. I max the group out at 6 people so that I can ensure they get the personal attention required to get them to their goal.
Another good question to ask the person you are considering is what do you offer in terms of support for your clients. For example I have my blog and I text message all clients every day or two telling them my calorie count for the day and asking theirs.
Your success will not occur unless your nutrition is in check and as you know, you are not eating with the trainer; therefore success and failure is determined out side of the gym.