Sounds like a new Output transformer has been fitted.
Like any amp mods or work, it will all depend on the quality of the work and the knowledge of the person who has done it. Although fitting a new OT is not rocket science, choosing the right one is important.
It could all be fine, or it could be a disaster zone. If it was me, I'd want a little bit more detail about what the new OT was, and who did the work. Ideally, even get to speak to the guy who did the work.
A change of OT will change the tone of an amp though, so it might be as well to make sure you can play the thing before any commitment to buy.