J.P. Sauer & Sohn, about 200,000 made, not rare. RCs have been going up but $500 still seems a bit rich, especially for a peened-markings example. If this is your first K98k then an RC isn't a bad way to become familiar with their function, examine all the parts, and shoot them. If it doesn't have a really good bore I wouldn't bother negotiating. If it has a good bore and you are looking for your first shooter K98k, then I'd point out the peened markings, mixed serial numbers (even though mixed serial numbers and Russian Capture are synonymous) and try to get him down at least $50, preferably $100. Pics would be great of course.
LC's right, Blicero is the resident expert. Hopefully he'll chime in.