You asked
Is the 7artisans m 35mm f 1 7 seagull worth buying used?
Here is what the site says about that.
From 7Artisans M 35mm f/1.7 Seagull: 7Artisans M 35mm f/1.7 Seagull: A prime lens by 7Artisans for Full frame cameras, 35mm f/1.7. Made with Seagull, in silver only. Specs - Maker: 7Artisans - Focal length: 35mm (prime) - Maximum aperture: f/1.7 - Made for: Full frame sensors - Mounts: Leica M - Stabilised: no - Autofocus: no, manual focus What it frames like - On full frame (Leica M): as marked, 35mm. Cameras it fits - Leica M9: Full frame - ...
From Buying used: Buying used: Cameras and lenses are built to last, and many photographers upgrade often. That makes the used market one of the best ways to afford good gear. A body that's one or two generations old is often most of the camera for a fraction of the price.
Quoted from this site's pages.