Most important:

DO NOT let a contractor decide if the plumbing is ok.

The worst thing you can do is deface a bathroom or kitchen, and leave decades old plumbing behind the walls.

Toilet flanges need to be updated, tub drains should be changed, kitchen lines should be updated, etc.

Nothing is worse than trying to save a few bucks withba simple deface, and a pipe or drain breaks, ruining the new bathroom.

Always call a plumber on remodels. Don't leave those decisions to a contractor.