When sourcing used Canon MegaTank or continuous ink supply system (CISS) printers, the most critical factor is the print head health. You should request a recent nozzle check pattern and a total page count (actuation count) from the supplier. A high page count (e.g., over 30,000 pages) may indicate that the internal waste ink pad is nearing its end of life. Ensure the ink tanks are free from leaks and that the tubing system is clear of air bubbles or dried ink clogs, which are common in poorly maintained used units.