I love MM, but is it worth twice as much as AFM?
No way!!

Ditto!! I actually prefer AFM for a number of reasons. Don't dislike MM, just can't like it enough to pay the ask.

While its true that the "value is what someone is willing to pay", I think people forget somethings that differentiate an ebay sale from a private/dealer sale. One vital factor of course if the actual or perceived need for back up service to a quite complex game - I remember worrying about this years ago when I decided to buy my first game. Another (I think even more important) factor is that an ebay auction lasts a week or so, but a dealer might have a game on the floor for weeks or months until the right buyer comes along. While a sought after machine will always do reasonably well on ebay, one less desirable will only do well if the right buyer is looking when your listing is around. I remember buying a car off a mate to get him out of trouble years ago. It was possible that I wouldn't get my $ back, but it worked in well with a trip I was doing. Then after I'd used it for that trip, I ran one add for more than he'd advertised it for in the same local paper and sold it at 7.30 that morning - because someone turned up having been searching for a manual version of the car. He just hadn't looked in the paper the week my mate had advertised it. (I gave him half the difference I got extra, he didn't seem that impressed, probably why I don't see that much of him these days!!)