I have a 3 year old sulcata that is almost 7 inches. However, heavily pyramided sulcatas will have shorter SCLs than they ought to. If the sulcata is that old and that small you may be dealing with an animal with MBD or kidney issues. They're tough little guys so may still make for a great pet with improved care, but you probably shouldn't consider breeding.
If it has a relatively smooth shell and no obvious signs of MBD, it is either a lot younger than they're claiming or it could be a California Desert Tortoise that they're trying to illegally "sell" by claiming it is a sulcata. Or, I suppose if they really don't know their tortoises they could be confused about what is... But if it is a CDT they are legally required to give it away, for free, usually to a rescue organization who will find a home for it.
Now, if it actually is a 10", 18 year old, fully grown, perfectly healthy sulcata I say pay the $100 because breeding that little guy to create a line of small-size sulcatas could make you a mint.
