Normalize the scope
Make sure each contractor is pricing substantially the same problem and finished result.
Separate known work from allowances
An allowance is not the same as a fixed price; it leaves room for a later selection or unknown.
Look for responsibility gaps
If one trade repairs the pipe but nobody restores the wall, the homeowner needs to know before work starts.
Ask how changes are approved
A clear change-order process helps prevent surprise additions.
Safety boundary. General planning information only. Do not open, dismantle or work on hazardous electrical, gas, structural, fire-protection or contaminated-water systems unless you are appropriately qualified and authorized.