Should repaired equipment be stated in the ad??

Buying something that is still supported by the manufacturer seems a sensible precaution when buying high priced second hand audio items, IMHO.

Otherwise, I'd suggest to go for "bargains" only and accept that there is a high degree of risk - especially as audio users damage things quite often (a blown tweeter, a fried amp or a bent stylus being par for the course for anyone serious at this hobby...in fact most loud house parties will usually blow a domestic speaker, as they just aren't up to that kind of abuse)

Maybe we need something like Vehix.com where all repair shops report repairs done. Just put in make, model number and serial number and you get a complete fictional, fabricated reassuring history. Or you get a dirty laundry list of replaced resistors and caps and tubes and face plates.

I just got my vintage KT 917 tuner back from Stereo Surgeons complete with before and after specifications and a professional evaluation. If I were to offer it for sale, I would not attempt to conceal this info. In fact, I would consider it a selling point.

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.