Power Amp Repair Question

They had a $100 estimate fee and I assumed I'd get an estimate with a diagnosis. After one month, the shop doesn't know what's wrong but says I lose the $100 if I want it back. I asked if they might know in 2 more weeks and they said probably not.
Rff000

If I were you I would not threaten them with any action until you have the amp back in your possession and off their property. Hopefully you have some type of a receipt that shows you paid them $100 to look at the amp and they would then follow-up with what was wrong with amp and what it would cost to repair it.

If so, and you paid the $100 using a credit card, then you can do a chargeback. If not I suggest you lick your wounds and move on, and be thankful you got the amp back, hopefully in the same condition you took it to them and not in a cardboard box in pieces.
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Forfeiting the $100.00 and getting the amp back might be considered money well spent considering the way they have treated you.

Paying an upfront fee for a repair estimate is customary in the stereo repair business. The fee is factored in when the repair work is done. If you decide to have the work done elsewhere then the estimate fee is forfeited. What you're paying for is the diagnosis of the problem and an "estimate" of the cost to repair it. Based on your posting, you never received the diagnosis so you should demand your money back or threaten legal action. As a last resort, take the gloves off and identify the shop on forums like this. Bad behavior isn't right and shouldn't be ignored.

I used to run a service shop and we still repair stuff now even though we are really a manufacturer. The shop in question is on thin ice with this one- no service rendered, and they want to keep the money?? No excuse really.

Your shop is not to sharp you got ripped off big time.