[Hot Vibrato]

I think it's disingenuous for the seller to tout a neck reset as a selling point. The guitar has had a butcher job of a reset in the past, but the action is WAY too high, so it now needs to be reset again, hopefully this time by someone with some skills. Assuming it wasn't done with epoxy, it can be removed and touched up, which would be at least $500-600 here in the U.S.. Sanding the bridge down is just not the proper way to fix this.

The seller didn't mention the frets, but they are probably in pretty bad shape. In my experience, when the action comes down on a vintage guitar (after a reset, etc.) the guitar will often have some pretty serious playability issues, due to the fingerboard plane being wrong, and because the frets are worn or unlevel. With the original frets, the chances are very small that it can be rendered into a great player. It almost certainly needs a refret , which would be about $400 or so.

If you want to play this guitar and not just look at it, you should count on spending another $1000 or so for a luthier to make it playable.

Edit: I noticed you were also looking at L-50s. I've seen a few of those old Syncromatics, and I've seen lots of L-50s. While the Gretsch obviously looks cooler, it has a laminated top, whereas the L-50 has a carved top. More importantly, an L-50 typically sounds way better than the Syncromatics that I've played (which didn't sound very good at all).