Should repaired equipment be stated in the ad??

Honesty is the best policy. Hiding the repair is not disclosing all the truth. Do unto others.................

I have found that there is so much anxiety about a miniscule scratch that if you said something was blown and fixed that you would have a tougher time selling . Many see repairs as a sign of abuse but it is not always the case.To the finicky it is a sign for a potential flaw.
To do otherwise, however is just to dishonest for me having been on the buyers end I appreciate an open seller. I will trust that person more than the guy who has used equipment that he always rates a 10 or at least 9.
As stated above a -non lemon- one time problem, resulting in a trip to the factory authorized repair center will usually end up as a full overhaul. The amp or other components usually sounds better than ever.
With speakers it's bit murky if you get a pair with one driver replaced there is asymetry due to break-in.
Most people don't reveal issues but I try to be as upfront as possible.
It is very easy for me ! I just keep everything I buy. The house is a bit overstuffed right now so a purging is in the works. The whole truth and nothing but!

Should I sell my car, I would not hide the number of miles or the vechicle, nor would I if the stereo gear was repaired. Besides, for some, repaired gear, rated properly may have a higher value. In that there may be less of a problem in the future, and the gear may last that much longer for the new owner.

A repaired piece of equipment should be worth more because it will likely not need to repaired again for a while more than one that hasn't been serviced, as Macro stated so eloquently.

I would tell everything I know about the equipment regardless of the consequences just for peace of mind. Some people have an easier time sleeping at night. The Golden Rule rules. Dan