Good Taxidermist
Go to their shop and look at the animals that are in their showroom. If you're getting a whitetail mounted, look at the whitetails that he/she has in the showroom. Don't let big antlers wow you, you need to be looking at the animal itself. If you're a hunter, you've seen live animals. You need to try to compare the mounts to live references and see how close they look to a live animal.
Then, ask yourself these questions:
Overall, does the animal look alive?
Do the colors around the eyes, in the ears, and on the nose look soft and natural or does it look painted?
Is the mount physically clean and groomed?
If you're having problems, take pictures of live animals with you for comparison. If you can't find any, ask the taxidermist for his reference pictures so you can compare them to the mounts. Any good taxidermist will have reference photos that he uses when he's putting a mount together.
Then, ask the taxidermist these questions:
Do you tan your skins (or do you use dry preservative)?
Can you alter a manakin for a specialty pose?
Do you guarantee your work?
If he answers no to any of these questions ... LEAVE.
DO NOT try to negotiate his prices, or ask for a discount.
For my repeat customers, I sometimes give them some kind of "extra" with their mount. But, when someone asks for a discount, I tell them I don't give discounts to anyone.
What it boils down to (and I'll tell a potential customer this too) "if you like my work, and you feel like my work is worth the price ... I'll be happy to mount your animal ... if not, I'll be happy to give you the names of other taxidermists in the area."
I know that may seem a little harsh, but I have yet to have someone walk out of my shop after looking at my work, then my prices, and then hearing that statement.
You should visit all your local taxidermists. Each one will have a little different style, and you may like one more than the others ... just for some miniscule detail.
Good luck in your search,
Kevin