You asked
Is the pentax hd d fa 28 105mm f 3 5 5 6 ed dc wr worth buying used?
I think it's a good used buy. It's a compact, weather-sealed full-frame kit zoom with autofocus, and it covers everyday shooting from wide to moderate telephoto. The catch is that it isn't stabilised and it gets darker as you zoom, so it's not a low-light specialist.
On a full-frame body like the Pentax K-1 Mark II, it frames as marked, 28-105mm. On an APS-C body like the Pentax K-3 Mark III, it gives you roughly 42-158mm equivalent.
As with any used purchase, buying used is worth a read, and budget for a new genuine battery with any used body.
Written by Claude from this site's pages.