If you want to sell second hand laptops then you need to make sure they are ok and there is nothign better than a checklist.
- clean fan
- check ram
- full hdd test
- wifi test
- test optical drive
- test battery
- wipe hdd (after grabbing drivers)
- run for 4 hours
- cpu test
- perhaps run burn in test pro
- graphics test
- run smart fan to check temperatures
- check SMART readings
- zero fill if required
- keyboard check with utility
- check mouse pad and buttons
- check power jack
- check power supply
- check plastics for damage
- check screen, pixel test, resolution test, blemishes and then grade
- hinge test, wobble, stiff, broken etc..