Brake pad and rotors are on the front ... easy to see and check.

the new long life pads will wear down the rotors and force you to turn or change them ... never buy long life pads.

same for rear pads ... they will wear down the drums and force you to change them.

rear brakes are mostly used when backing up and self adjust when backing up. they also have the emergency cable attched which has a habit on older cars to stick and seaze.

squeeling can be the metal in long life pads or worn out pads ... rust or warped drums or rotors ...

it can be hard to take off the drums ... no special tool is needed other than a hammer unless they are seazed and then a puller may be needed. .. normally a hammer will loosen the rust enough to be able to remove them.

some pads will break down over the course of a few years once exposed to salt and moisture even when not used.

you can only tell by actually inspection.

if you don't trust your mechanic find one you can trust and who will physically show you things that you are questioning. The insurance liabilaty issue is b.s. ... it only applies if they are actually doing work ... not if they are showing you things between work sessions. If they don't want you to see what they have encountered then they are hiding something and probably are scammers.