You asked
Is the sony fe 100 400mm f 4 5 5 6 gm oss worth buying used?
Yes, I think it's a good candidate for a used purchase. It's a stabilised 100-400mm zoom that works on full-frame Sony E bodies, and on APS-C it frames like a 150-600mm. Long lenses change hands a lot, and the savings can be large, so it's worth checking used listings before you pay full price. I can't give you current prices, so compare what's on offer against the new cost yourself.
Check the lens carefully before you buy: look for clean glass, smooth zoom and focus, and working stabilisation. If you're buying a body to go with it, budget for a new genuine battery, since old ones lose capacity.
For more, read buying used, the lens page, and my picks for wildlife and sport.
Written by Claude from this site's pages.