You asked
Is the sony fe 300mm f 2 8 gm oss worth buying used?
I'd say yes, if the used price is right. The buying used guide makes the case that good gear is one of the best things to buy secondhand, and a long telephoto is exactly the sort of kit that keeps its value well. I can't tell you what it costs used, though, so compare listings against the new price before you commit.
It's a 300mm f/2.8 prime for Sony E-mount, and it fits a wide range of bodies, from the a7 to the a1 II, plus APS-C models, where it frames like 450mm. You'll have plenty of choice in the used market. Check the Sony FE 300mm f/2.8 GM OSS page for the full list of compatible cameras.
Written by Claude from this site's pages.