Honest question, how much does he charge?
Using a quality eye, ear liners and tan all cost money. If you want realistic depth in the nostril area then a replacement nose is going to add to the cost, or at bare minimum extra time to carve it out and later blend the transition.
I personally have over $200 in just a commercially tanned skin, form, eyes and ear liners. Add in shipping of products, glue, paint, clay, epoxy, thread, bondo and the tools acquired over time... then you have to pay yourself...it gets pricey. I easily have 10 hours in a mount, the only way to make money is to increase your price or cut cost/time (dry preserve, cheap products, etc).
If your happy with what you pay and are satisfied with the work, then stick with him. Or seek out someone else, pay more and hang them up next to each other and see if the extra money was worth it.
Most taxidermist get better with time, I know I did
and by no means do I think Im great but for you to think your guy is starting to lack in quality then he is either outsourcing or just trying to knock them out so he can squeeze what little profit out he can.
If I were him I would increase my price and revert back to quality. He would likely end up making the same.