If they're saying 50L then it should be an LK50, bigger brother of the LK35 little brother to the LK70; if it's a 50 the inside of the top lid will have Haglofs as well as the three crowns, which you could always check with the seller ~ Haglofs made the 50 and 70 versions. A good and solid pack which, for some reason, has no hip belt

. Because of the lack of ability to shift the weight to the hips the weight's all on the shoulders ~ and when fully laden can become very uncomfortable very quickly! IIRC ALICE LC2 belt and straps* are a common mod and are pretty much straight swaps
The pack is bombproof, if heavy

. The older versions of the LK's are 'proper' canvas, the newer are more 'polycotton canvas', Endicott's basically proved that a top notch newer version is basically waterproof (they filled one with water

~ iirc they were happier to call it 45L ~ the 50 comes from the shape of the lid, angling the lid increases the capacity.
* Oh yeah, the pack's straps have no real padding, I've not found an issue with this unless I've had to carry kit for a long weekend plus an excess (10 - 15L) of water.
Not a bad price at all ~ providing is as good condition as the pics suggest.