1904 National Cash Register Model 138 Nickel Plate Art Nouveau Case

It depends on how much restoration was done (i.e. how much of it is original) BUT I will say that I have NEVER seen one of these sell for less than $900 Canadian Dollars, and I have looked at them. Usually they are in the $1200+ range. So either you have a very good deal, or it's mostly a new product with a few bits of old in it.

So if it's in good shape, and mostly original (he should be willing to document what was done to it for you and often keep the replaced parts with the machine, as part of the provenance) I'd jump at the $600 price myself. The reason you want the provenance is to prove that the 'new' parts are the result of a restoration, and not an attempt to 'make a fake'. You want as much of the history as you can for that. For example if you can, keep the original owner information with it, who bought it when sold (receipts) etc. It creates an ownership trail that helps authenticate it.

Hope this helps!