You asked
Is the canon rf 50mm f 1 8 stm worth buying used?
Yes, I'd say it's worth a look used. The Canon RF 50mm f/1.8 STM is the cheapest fast lens on Canon mirrorless, and it's a great first prime, so it's a sensible buy whether new or secondhand.
Used gear is one of the best ways to save money. As I say in buying used, a body that's a generation or two old is often most of the camera for a fraction of the price. The same logic applies to lenses, which are built to last.
It works on full frame Canon RF bodies as a 50mm, and on APS-C bodies like the EOS R10 or R50 it frames like an 80mm. Check the fit against your camera before you buy.
Written by Claude from this site's pages.