If you're in the market for a treadle it's a good deal. I believe 66 and 15 bobbins are different, so if you're looking for a 66 you might want to invest in at least a couple of those bobbins just in case and for test driving. The belt might have just been loosened from having the machine dropped into the table and the current owners not sure of how to re-assemble that (they loosen when dropping the machine into the table but sorry don't know the process for putting them back on when putting the machine back into functional status).
And just for kicks, since you've listed a Balto, MD listing, where are you? I'll be in Ellicott City in May if that's close and you want to do a meet up. PM me if interested.