How to test a used E-30?
Here are some of the things I look for in a used E-Series:
1. Check service menu for number of shutter releases and damage codes. If any damage codes, send camera back.
2. Insure you can format, write to and read from both CF and xD cards. Note: even though nobody uses xD cards anymore, an InOp xD slot will reduce what you can get for the body when you decide to sell it later on.
3. Shoot both light and dark backgrounds out of focus, then review both shots to check LCD for bad pixels.
4. Review the same two photos on your computer to check for bad pixels. Remap sensor and repeat if needed.
5. Set Aperture priority and F16. Press and release DOF preview button while looking through viewfinder to verify proper opening and closing down of aperture.
6. Exercise tilting LCD panel to all various positions and verify info on screen does not change due to poor electrical contact.
7. Exercise mode dial through P/A/S/M and all other modes and verify proper mode is selected every time indicating clean electrical contacts. While in each mode, take a shot to verify proper operation.
8. Verify flash fires and produces properly exposed shots.
There are certainly many other things to check but these are the ones I focus on when inspecting a new (to me) camera.