If the deposit is forty to fifty percent, negotiate or ask about a thirty-percent deposit followed by ten or twenty percent more when the job is half complete, and the rest upon delivery. To me it suggests he has more interest in your cash than in acquiring you as a client, or than in your satisfaction. Also, if the mount is to be shipped, ask whether packing and crating are included in the price. Most times they aren't, so ask what the cost might be, and make sure that quoted price is included on your deposit or cost agreement. Also get an estimate of shipping costs.
Some taxidermists work in teams.
This is okay as long as both are highly skilled in their craft. Ask about added costs, such as panels. Panels can add considerably to the cost of a head or shoulder mount, depending upon how they are made, who makes them, and what they are made of. Ask to see the various types, and once you make a selection, get a price in writing. Also, make sure the price quoted will be the real price charged in the event the mount takes longer than expected to finish, or if there's a price increase.