Most 98 Mauser rifles used a 22 pound striker or firing pin spring. The 30 pound spring is available for use in sub freezing temperatures or with hard primers. As long as the firing pin protrusion checks out ok, either spring is fine.
These can be great hunting rifles in their original caliber IF they are in good condition.
The major concern is the bore condition and headspace. Most of these rifles have seen extensive use, and have been exposed to corrosive ammunition. Check the bore if you can, especially the area just ahead of the chamber. Inspect the crown of the rifling at the muzzle.
Excessive Headspace is more difficult to check without proper gauges, but an easy way to explain it is when the 2 locking lugs on the bolt have been gradually pushed backwards into their seats in the receiver. It happens to all bolt action rifles over time, but sometimes becomes a problem about the 3,000 to 4,000 round mark.
Start with the bolt in its closed position, lift the bolt upward to unlock it, then push it back down to it's locked position SLOWLY. If you feel things are tight when the bolt handle is up, but feels significantly looser when it in the down, or locked position, this is a bad sign. If you can feel the bolt handle move backwards (towards the butt) just before it reaches it's closed position, the recoil lugs and their corresponding seats in the receiver are probably set back.
None of this is 100% precise, but it will give you some way to judge the condition of the rifle without a full gunsmith inspection.
In my opinion, if the rifle is in good shape and can be purchased for $600 or less, I'd consider it. If it needs a rebuild, or you want another caliber, I'd pass. Unless you do the work yourself, you'll end up spending more than many new rifles would cost.
