You asked
Is the canon rf 75 300mm f 4 5 6 worth buying used?
Yes, I'd consider it used, though it's already a budget lens. The Canon RF 75-300mm f/4-5.6 is cheap and light, but it has no optical stabilisation and gets darker as you zoom in, so check that the copy you're looking at is in good shape and focuses cleanly before you pay.
Used buying is a good way to get gear for less, as I explain in buying used. It fits well with this lens because it's already inexpensive, so the saving is smaller. If you're pairing it with a body like the Canon EOS R8 or R6, buy the body used too, and budget for a new genuine battery.
Written by Claude from this site's pages.