I don't recall seeing very many off-center mercury dimes

Cool! At first I thought the obverse had rolling machine damage, but that must be from the collar (the reverse die was the hammer on Mercury dimes).

i found one that was 5% off center and sold it for $100. can't imagine what this is going to sell for!

Fred Weinberg usually has a few in inventory http://www.fredweinberg.com/ he sells them for around $500.00-850.00 on average.

Just saw my friend Fran Leone has a really nice double stuck Mercury for sale at a fair price, I'm not after one but if you are here you go:
http://1793.com/inventory_errors.htm
Tell him I sent you, (not that I get anything other than a thanks from him), Frank is an honest and great coin dealer!

That is sort of odd, isn't it. I've got well over 3,000 Mercury Dimes and the main thing I've found in the way of errors is that about 25% have rotated reverses. Anywhere from a few degrees to about 90. None are off centered at all. Seldom any RPM's, double died or some of the more common type of errors. Lots of large and small mint marks are popping up lately though. Sort of the same thing with Buffalo Nickels too.