There's also a website where outfitters are reviewed, I forgot the name
Google Outfitter Reviews and you'll find several sites. Just be careful because the outfitters can be sponsors or provide free hunts and review dates can be old. Most sitesnwill charge you a subscription fee. Most do not have enough reviews to be useful.
Most states and provinces have an outfitter organization that keeps track of complaints, though not all outfitters belong and not all upset hunters contact them.
Realize too that some hunters just have unrealistic expectations or just want to blame their own failures on their guide or outfitter. I'm sure the guys on the forum who have guided could tell you stories about that until the cows come home.
When you buy a guided hunt you buy an opportunity and an experience, not a trophy. There's a big difference. There are a lot of things outfitters and guides cannot control, like weather, your conditioning and your ability to shoot accurately and fairly quickly. There is no way to guarantee either your experience or your trophy unless you want a high fence hunt, which is not really hunting.
Our forum is a good source of honest feedback, especially if you PM guys who have experience with an outfitter. Ideally, you want someone who has guided for them.
When you decide which outfitters to call, I always say not to ask for references - ask for the contact info for all hunters in the last three years so they can't cherry pick. If they won't agree to that, move on.
Mike Eastman has a great chapter in his elk book about finding a good outfitter and what questions to ask them. I thought that chapter was outstanding and worth way more than the price of the book. I highly recommend getting that book no matter what species you are interested in booking a hunt for.