Apple recognized repair service asking for password?
It's pretty common for a repair facility of any kind to ask for a username/password for the sake of verifying functionality. This is why it's always a good idea to have a separate administrator account setup for these kind of tasks. Usually an "Administrator" account with a unique password works.

I've worked in the IT industry for almost 20 years, and I've always appreciated when a user has a separate admin account. It makes working on the machine faster as there usually isn't as much stuff loading on start up. It also keeps me from seeing any of your information, which is great for legal reasons.