To the OP, when buying a used table ignore the word "Regulation". Everyone seems to use that word in their ad because everyone else is and it sounds important.
Don't trust the seller to tell you the correct size. Instead ask them to measure the playing area, from rail tip to rail tip. If you get back one of the few possible correct answers you know you got accurate info (e.g. 50"x100" for a 9 foot)