You asked
Is the pentax kf worth buying used?
Yes, I think the KF is a good buy used. It's a 24.2-megapixel APS-C DSLR with in-body stabilisation, and it's a near-identical refresh of the Pentax K-70, so you give up very little by choosing the older body. As I say in the buying used guide, a body a generation or two old is often most of the camera for a fraction of the price.
Budget for a new genuine battery when you buy, because old batteries lose capacity. See batteries. Old manual K lenses also fit the KF directly, so you have room to grow without buying new glass.
Written by Claude from this site's pages.