A couple thoughts to add on using a booking agent.
I have used booking agents in the past. In many ways they can be good, but there is a big down side. Booking agents create arrangements with outfitters where they receive money if they book a hunt for the outfitter. The downside of that is two fold. First they will only book for outfitters they have an arrangement with so you aren't necessarily looking at all your options. Second, some of the very best outfitters don't use booking agents simply because they don't have to. They have developed a good enough reputation where they stay booked years ahead on word of mouth referrals or repeat customers. That is the type of outfitter I want to find. When I have used outfitters in the past, all of the best ones I've found, I found doing my own research.
Here is a specific example with a big name booking agent. Years ago I did an enormous amount of research on a stone sheep hunt for my dad and I. I picked the outfitter I thought we should use and contacted a booking agent. They said they would not recommend them and we ended up booking a Fannin/Dall sheep hunt through the booking agent, which turned into a Dall sheep hunt since he really did not have many Fannin rams (stone/dall cross which qualifies for a stone in a grand slam). A few years later I resumed my research for a stone sheep hunt looking at every stone sheep outfitter in BC and again chose the same outfitter. That outfitter was taking around 20 stone rams a year.
I am a huge proponent of doing my own research when it comes to hunting.