The .257 Roberts is an excellent cartridge and I've seen it used by at least a dozen different hunters take caribou to 200 yards with rifles so chambered...
I have two rifles built around it, one a light weight sporter and the other a heavier varmint rig and it performs well in both...One started out as a Swedish Mauser and the other an Argentine Mauser...
The price may be just a little high so barter with him, almost no price is "set in stone" or maybe have him through in the cartridges, brass & dies (if reloader), carrying case, sling etc. to sweeten the deal...
Can he produce a target for you to see or will he let you "take it out for a spin"?
Sorry, didn't see the second page and that you got it already...Wear Well!