Well, I don't need one, but I figure the manufacture date is later, so if the thing is in decent shape it has a chance at a longer life. My PS2 no longer plays PS1 disks and my attempts at fixing it haven't worked. I'd have just dealt with it if I didn't pay more money than the average used Playstation goes for, but $40 is too much for one that isn't in all that great shape. Not to mention he didn't package it properly, so I wouldn't accept it either way at this point unless he sends me a check.
Also, PSOne isn't really popular terminology. You don't see it called that very often, or at least not spelled that way. PS1 is more common, and that's not the actual name of the item, hence no confusion. Besides that, there are separate listings for PSOne and Playstation (original) on Amazon.com. There's no excuse.