Diagnostic teardowns and approval
A technician may need to open panels or remove parts to find a problem. That is normal, but it should not be used as pressure.
Ask before teardown
Before the technician takes anything apart, ask what the diagnosis will cost and whether reassembly is included if you decide not to repair.
Get the diagnosis first
Ask for the diagnosis and a written price before any repair starts. Approving work in steps keeps you in control.
Second opinions
For big repairs, you can pay the diagnostic fee, keep the written diagnosis and get another company's price. Ask for the diagnosis in writing so the next company can check it.