The fault itself. A flapper renewal and a flange repair are different jobs in time, parts and risk, even when the symptom — water where it should not be — looks similar.
What testing finds. Some faults are single; some arrive with company. A base leak can be a wax ring, a flange, or a floor problem, and the honest scope is only known once the toilet is lifted and the flange is seen.
The model and its parts. Common models use widely stocked parts; older or brand-specific mechanisms may need parts matched and ordered by model.
Access and condition. Seized valves, corroded bolts and previous repairs done badly all add time, because the new work has to be built on a sound base.
Whether the toilet stays or goes. Where testing shows a toilet at the end of its life, the conversation changes from repair scope to replacement — before money is spent on parts for a toilet that should not receive them.

How the process protects you: the fault is tested first, the findings are explained, and the scope of work is agreed with you before the work begins. No work proceeds on an open-ended basis.