A practical checklist for testing any used keyboard before you hand over your money. Covers dead keys, key chatter, ghosting, rollover, latency, and physical inspection, each check taking under a minute with free online tools. From the keyboard testing guides at https://keyboardtesteronline.com/ , with the full walkthrough here: https://keyboardtesteronline.com/how-to-test-a-used-keyboard-before-buying/