The bench is full of things that belong to other people. Every item taken in needs a record of whose it is, what was agreed and when it was promised, because a saddle nobody can identify after three weeks is an expensive conversation.
A commission is a long relationship. Deposit, choice of hide, fitting and final payment are spread over months, and without staged agreement the workshop finances the material for the whole period.
Hide does not cut like fabric. Each skin has flaws and a usable area that varies, so the material cost of two identical orders differs, and quoting from a fixed figure loses money on the awkward ones.
Travel is part of the fitting price. A morning driving between two yards is unbillable time unless it was planned, and grouping appointments by area is what makes the visits pay.