Welcome to the forum, - regarding your question, you will have to be a little more specific.
If the "K98 shotgun" is one of the shotgun conversions done with leftover Spandau marked Gewehr98 receivers then they are not too rare or desirable. They do have a following, several articles have been written about them, they come in a number of variations, one of the better known is the Geha 12 gauge shotguns manufactured by Gebr. Rempt in Suhl (AKA Remo Gewehrfabrik), though I believe they were made by many small firms in the interwar period. There certainly are many variations known.
Anyway, they can be dangerous to shoot I hear, not a fundamentally flawed design, but something about the bolt construction can lead to a dangerous situation. Seek out Google for these shotguns, there are a number of good posts on other sites about them. I don not follow them, few military rifle collectors do, but I do follow the companies as thoroughly as possible.