Should repaired equipment be stated in the ad??

Serviced or repaired, I don't know,
But I'll take a Threshold amp upgraded by Jon Solderbreg.
I also prefer a car with full service records!

That would be ideal, and I would personally feel ethically bound to do so. However, caveat emptor is applicable here. When you buy used you are getting the product for less than you could buying new. The risk of buying a repaired item or a defective item is part of that deal. You are not getting a dealer warranty and, in most cases, you are not going to get a transferable manufacturer's warranty. As with anything, there are pros and cons. I would not be surprised if someone sold a used item that had been repaired without disclosing the repair. There are of course reasons other than cost savings for buying used rather than new, such as buying vintage items that are no longer available. Same risk benefit ideas though.

Can you honestly say that you would buy repaired one of two identical units sold for the same amount on Audiogon??

I think it depends on the equipment in question. If it's a 1 or 2 year old component, very high end, I may be hesitant, especially if it wasn't the factory performing the service, or it was anything but a minor fix.

I'm somewhat of a bottom feeder and have purchased fairly old gear. (eg my B&K M200 amps - I had 8 of them at one time) I wasn't as concerned about repairs as I was current condition. And frankly when you're buying something from a second or third owner you can't truly know the repair record, although the fact it's not an original owner item will discount the value anyway. Further, if a component was recently serviced by the manufacturer or reputable tech, it may indeed have higher value (eg, an older amplifier newly recap'd) than one that is original/never serviced.

In any event, IMO, if repair record is important to you as a buyer, you should ask, and not expect it to be disclosed in the ad; and if you're a seller and are asked about the repair record, A'gon's etiquette policy should oblige you to answer honestly, accurately, and completely. (though the policy below may not be worded strongly enough)

Expected Etiquette:
All Audiogon members are expected to conduct themselves in an honest and civil manner.

Bdgregory - So you would really select and pay more (worth more to you) for the repaired unit (everything else being equal). Are you serious?

Or maybe when you find out that you bought repaired unit you should call seller and thank him for that (higher value)?

According to this one should advertise repairs done to the unit since they increased its value. We don't have problem anymore.