You asked
Is the sigma 105mm f 2 8 dg dn macro art worth buying used?
I don't track used prices on this site, so I can't say whether a given listing is a bargain. The general case for buying used is strong, though. As I explain in Buying used, good gear lasts, and used kit can give you most of the camera for a fraction of the price.
This lens is a full frame macro: 105mm at f/2.8, autofocus, no stabilisation, for Sony E and L-Mount. The catalogue page lists every compatible body, including APS-C models, where it frames like 158mm. Check the condition of the lens and make sure the mount matches your camera before you buy.
Written by Claude from this site's pages.