Absolutely changing cords with power still on would cause this!!! An unfortunate occurance to be sure, but not your fault, NOR your responsibility. This would be like selling a used car, then taking responsibility for the repairs caused by the new owner putting sugar in the gas tank.
If you can assist by helping the purchaser find a reputable repair shop, then by all means do so, and if you are willing to offer him a ride to and from (assuming he needs that) that would be extremely accomodating. However, paying in any way, shape, or form for a problem so obviously caused by the new owner is simply too generous unless a repair tech can tell you that beyond question the Rega was about to blow (and we both know that is not the case).
I certainly applaud your noble conscience, but this gentleman has made his own bed in this case - there is no need for you to have to lie in it too.
If you can assist by helping the purchaser find a reputable repair shop, then by all means do so, and if you are willing to offer him a ride to and from (assuming he needs that) that would be extremely accomodating. However, paying in any way, shape, or form for a problem so obviously caused by the new owner is simply too generous unless a repair tech can tell you that beyond question the Rega was about to blow (and we both know that is not the case).
I certainly applaud your noble conscience, but this gentleman has made his own bed in this case - there is no need for you to have to lie in it too.