You asked
Is the sony fe 50mm f 1 4 gm worth buying used?
I'd say yes, with one caveat. This lens fits a wide range of Sony E-mount bodies, full frame and APS-C alike, so you can match it to a used body without worrying much about compatibility. The lens itself is a sensible thing to buy second-hand, since lenses hold up well and a one- or two-generation-old body often gives you most of what you need for much less. The site doesn't list prices, so check current used listings yourself before deciding.
Whatever body you pair it with, budget for a new genuine battery, because old ones lose capacity. The buying used guide covers the rest of the checks, and you can see every body this lens fits on the Sony FE 50mm f/1.4 GM page.
Written by Claude from this site's pages.