A buyer who knows what they are doing opens “About This Mac” first, checks the number of charge cycles and the battery condition. If there are more than 800–1,000 cycles and the system says “Service Recommended”, that is a solid reason to negotiate the price down.
The second checkpoint is the display and the body. Flex cables, keyboard marks pressed into the glass, hairline cracks near the hinges. All of it shows at a glance, and not all of it can be fixed. The ports are a story of their own: oxidation on USB-C contacts looks like dirty smears, and it puts buyers off just as much as a damaged lid.
Next come the drive and the system. A savvy buyer will run Apple Diagnostics, check the drive's SMART data and sometimes software such as CoconutBattery. Glitches, heat under light tasks, noisy fans — together they leave the impression of a tired machine.
The nastiest issues are the hidden ones: traces of liquid, repairs done carelessly on the board, a lid that was opened and put back not quite right. Some MacBooks run perfectly until you launch a heavy graphics test or restart them a dozen times in a row.
So before selling, it makes sense to run full diagnostics — from battery condition to cleaning the cooling system. It takes little time but adds confidence for you and for the buyer. A tidy, verified MacBook sells faster and for more.