Best Buy Electronic Store deliberate misguidance?

I need some guidance on handling a problem I recently experienced through Best Buy. My mother took her computer in because it was acting extremely sluggish and freezing up. Initially they told her it was $59.99 for a diagnostic exam. Later in the week she recieved a phone call telling her to fix the problem they needed to run extensive diagnostics and repair which would cost an additional $199.99 because they found viruses. They took our the viruses and installed some childsafe software and the total came to $370. They then called and said they discovered it was actually a bad harddrive and it needed to be replaced (an extra $100). Since replacing the harddrive will completely eliminate the work they did previously, I am wondering what our rights, as customers are. She specifically asked if she it was cheaper to buy a new computer and was told her computer is good and should last about 3 more years. Should they have been able to diagnose the bad harddrive from the inital tests

Best Buy Electronic Store deliberate misguidance?microsoft office

Report it to a manager. Demand an itemized invoice of precisely what they have done, how they have done it and when they did it.

I have never had nor heard in all my years, any good experiences when sending a computer to a "professional" for repair. If at all possible find someone you know and trust. Or just ask us: we're geeks for free.