I paid $400 for mine last year. That was like new, no box. Shoots great, looks very Untactical. I like that. Most people mistake it for a 10/22.
I put 50 rds through it and the factory buffer showed noticeable deformation.
On advice of MY experts I ordered a new buffer and recoil spring.
I ordered from 'Blackjack Buffers'. Their model '821-B Spring and Buffer Kit'. This includes their buffer (blue) and a Wollf 21# extra power recoil spring. $24.50 shipped.
I've put 400 rds through it with the new buffer and it still looks like new. The heavier spring is recommended for use with '+P' ammo. It is flawless with anything from WinWB to Cor-Bon +P.
It groups Slightly better with 124-147 gr but not enough to buy special ammo just to feed the Marlin.
As you can tell, I don't like the Camp 9 at all! But you ain't gonna get mine for no $500!

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Field Researcher. IGC