Personally, I would be extremely suspicious of a barrel that had been removed after just 20 rounds. At least, without a reasonable explanation by the owner. Such a low round count shows virtually nothing of a barrels' potential, so the reasoning behind removing it would have to extraordinary! Having been on the losing end of such "deals" too many times in the past I would be unlikely to even consider such a deal at this point of my life. At the least I would have plans in place to replace it with a new barrel if it didn't work out.
Cheers,
crkckr