What CanadianAR and collector67 have pointed out is totally correct, but I'm one of those people that maintains the fact that captured rifles are still quite collectable. They're still made from WWII German parts so they carry quite a bit of history. As CanadianAR pointed out, an all matching K98k goes for $1500+ while the average RC K98k goes for about $500. So depending on what you'd like to do with the rifle an RC may be a more viable option. If you want something with the most collector's value, try to find an all matching one but if you want something that you'd like to casually shoot/hunt with, a RC is the way to go.
I picked up a pretty decent captured rifle a few days ago. It's a 1938 dated code 27 ERMA. The waffenampts have not been peened, there is no Russian X on the receiver, there is no black paint on the parts, there is minimal electro penciling and the stock set is actually completely matching (the stock, hand guard, both barrel bands, the stock spring, butt plate, bayonet lug and again with the waffenampts are intact in the wood).
If you've got $1500+ and want a K98k then go for the all matching one! But if you are kinda strapped for cash, or want to shoot/hunt with it, then the RC isn't always a terrible option.
Here are some pics of the one I just picked up: