The Marlin Camp 9 has problems. Research them on the internet. The rifle has a plastic buffer piece, that the bolt slams against when it goes rearward. This is apparently a source of lots of problems. People have reported that this piece breaks in as little as 400 rounds, which isn't very many rounds considering you are shooting the 9mm.
If this piece breaks, where are you going to get a replacement? Marlin stopped making this rifle several years ago, and I doubt that they are stocking this part. I read that some company use to make a better quality, polymer, replacement part, for a pretty high price, but that this company isn't making them anymore.
Also, this rifle was made in .45 caliber, and apparently, this stouter round was routinely causing the stock to split, right where the back of the receiver meets the stock, at the top of the grip.
So, I would do alot of research on the complaints and problems posted on the Net before buying a Marlin Camp 9. Especially since there are apparently alot of other good reliable 9mm carbines out there.
Regards, Mannyrock