That would be a wonderful question to ask. If they are ONLY replacing the circuit board, a clean room really isn't needed as the drive internals are not being exposed. Anyone can do that no problem. Done a ton myself in dusty environments.
If the circuit board doesn't fix the issue, someone needs to go inside that drive and either physically move your discs to another compatible drive or replace the broken part(s) with suitable working ones. This should be done in a clean room. If anyone tries to tell you otherwise, remember it is YOUR data that is being compromised, not theirs and do what you feel is appropriate. Many times, recovery companies will ask you to ship, along with your 'dead' drive, another similar drive. (same model, capacity, etc) so they can simply move the good parts from the 'dead' drive to the new drive. It saves a lot of time and hassle and is cheaper than trying to manually extract pieces of data from a failing drive.
Any questions post back.