You usually CAN use a full frame lens on a crop body but a crop sensor lens will not work on the full frame

Example
Molly shoots a 40 D (crop sensor body) and uses a full body 500mm,or a 100-400 but her 10-22 (crop lens) will not work on my 1D (full frame)

Her 10-22 is the equivalent of a full frame 16-35 (1.6 crop factor x 10mm= 16mm and 1.6 x 22=35mm)

The 16-35 on her camera gives the following field of view
1.6 x 16=26mm and 1.6 x 35 = 56mm

Wide angle is usually defined as 28mm or smaller

So using the 16-35 barely qualifies as wide angle if used on a crop camera.

This article does a decent job explaining it
https://yourphotoadvisor.com/full-frame-lens-on-crop-sensor-this-is-what-happens/

There are always people that trade in perfectly good used cameras to buy the latest and greatest which means you can pick up an older model for reasonable money.
Considering most digital cameras are rated for 100,000 or more on a shutter, they have a pretty long life.

Something to think about
I have bought several used camera bodies but have always bought my lens new