I've been looking at getting a bayonet for my RC K98. The first thing that stands out to me are the grooves in the grips and lack of loop on the tang(?). Then markings of course. Figure it wouldn't hurt to get an opinion on one I've seen. Any other easy things to tell right off the bat?

http://www.ebay.com/itm/German-WWII-Mauser-Bayonet-and-Scabbard-Matching-Fnj-1943-Knife-/291547492213?hash=item43e195af75

I'm not sure what you're asking. K98 bayonets aren't hard to find and they generally don't command a large sum of money in the grand scheme of bayonets unless they're a rare variant. As such, they aren't really faked, either. I know of a few repros but they're pretty easily identified and generally they aren't passed off as the real thing.

The Germans didn't use checkering on their bayonet scales. They used grooves like what is pictured. They also didn't use a loop to secure the bayonet. That long mounting stud on your rifle fits deep enough into the bayonet that a ring isn't  necessary.

I'm no knowledgeable either, when I need to learn something about bayonets I go here;

http://milsurpshooter.net/forums/79/The-Bayonet-Collectors-Forum/The-Bayonet-Collectors-Forum#.VdydPuDn8v4