Something to keep in mind is that most of those rifles are at least 70 years old and some are approaching 100. Many saw at least one world war and often regional conflicts after that. So many of them are worn and tend to have a little character. The others above have pretty nicely spelled out what to look for with the bore. One safety thing I'd consider is getting the headspace checked, especially if the bolt doesn't match. A gunsmith can do this or if you plan on buying more Mausers you can invest in a set and do it yourself. Plus if you plan to buy more milsurps I suggest getting a C&R, it's only 30 bucks, not really any harder than a normal background check to get, and will come in handy if you want to buy more.

Also, some online outlets have Yugos fresh out of the crate. While you may not know what you will get as they grab them out of a crate, I do know that while on the high side Aim has matching Yugoicon M48s which probably aren't a bad starter Mauser as a shooter or in a collection as while Yugos are common, having a matching gun (not sure if they are original matching or renumbered after a rebuild by the arsenal) is always nice. If not several other outlets have M24/47s for around, or a bit less, than that one on Gunbroker. Having the bayonet is nice if you have all the other accessories but I don't think Mausers were generally sighted with them (someone correct me) so it's not a must have to me, though if you value that at around $50-70 that puts the gun at $230-250 which is not bad. With those of course you'll have to clean up cosmolineicon but that's part of the fun of buying a surplus gun! Just depends on what kind of Mauser you want.