Selecting an outfitter is not unlike making any major purchase - you are pretty much on your own because no outfitter is going to advertise that he is a rip-off artist with poor equipment, incapable help and no critters in his area. Word of mouth is a great source, particularly if the person is a friend or acquaintance. Check with guys at the fish and game or gunclub, if any had great hunts or got ripped off. These web hunting forums are becoming a great source of info. Clubs like Safari Club and N.Am.Hunting Club also have reference info that might help, check some past issues of their magazines.
Remember, there are a lot of variables that an outfitter cannot control, but good outfitters are on top of **** near anything that happens during their hunting season. They want you to succeed as much as you do, they want to make your hunt well worth the bucks. Like any pro, they are good because they know what works, "they been there".
Perhaps I could make a few suggestions and other fellows who have had positive experiences could help also.
First, not a bad idea to contact the state or provincial wildlife agency to get the name of the elk or bear or antelope or whatever biologist or specialist on staff. Track down such a person or someone that they could recommend for info on starting your selection as to region, area and outfitters. Also contact the guides and outfitters association if there is one, most jurisdictions have one and they are getting pretty good websites up.
Get some info as to what the population situation is - stuff like recent winterkills, CWD, drought, fires whatever should be considered. Although the guy will be a resident ask him where he would send his out of state buddy for an X hunt.
Go to sportmans shows, the ones that outfitters attend and talk direct. They are there to do business, get lots of info and references.
Check the web, more and more hunts are being booked that way. Another possibility is to simply go through a booking agent. Again, there are good ones and there are crooks, buyer beware. Check into their references just like you do the outfitters. Some of these guys are just plain great - they take care of a lot of the ******** because they only represent top-notch outfits. Some agents just want your money, be careful but consider an agent - Cabela's even does this type of stuff, they are going to do a good job I expect.
Either way, talk to the agent and outfitter direct, and ask for some recent references and make the contacts. This is money well spent, it is part of the hunt preparations. Ask lots of questions and keep a dedicated notebook and write it all down so you don't mix things up.
Make sure you also have a base list of questions to ask the outfitter when you first make contact - how much experience, overlap the questions with the ones you ask the references. When you talk to references ask how many times the individual has hunted with the outfitter, success, competetence, gear, weather, work from a list and go down it one by one and write it all down. Ask questions that will give you crossreferences on topics, get info from several guys on each topic and compare to what the outfitter said.
In all likelyhood you will start to get a gut feeling about who you want to trust. Take your time, if you don't feel totally confident keep working at it. Remember, some outfitters are not naturally salesmen, they just might not be smooth talkers or they might get their wifee to do the talking. Don't get snowed by the ******** artists.
When you get down to the nittygritty try to get on a first name basis and be HONEST. Make your expectations crystal clear but be realistic. If you are out of shape, can't shoot, afraid of heights, alergic to milk or whatever - tell him, he needs to know some stuff about you even before you get together.
When you get into camp the outfitter will be sizing you up as much as your are sizing up him and your new surroundings. He will be guaging how fit you are, your personality, your equipment, your eagerness and other stuff. When they suggest that the hunters check their rifles, they are assessing how safely and confidently you handle your firearm, plus if you can shoot worth a ****. They know that sometime guys who punch them all into one hole at home can't hit **** when the target is breathing. (That is a good reason why we should shoot as much as possible before such a trip, not just the week prior - and definitely not from the **** bench.)
I am fortunate to hunt with a lot of outfitters. My son and I work with some of the best in western Canada with our website business. No doubt I haven't covered the whole picture here but I hope that some of this is of interest.