Ask HN: Your Experience Buying / Selling Used Macs

It seems to me that one of the nicer parts of having a mac is that it maintains some significant resale value a few years later

I'm making a spreadsheet of the cost/year of ownership of various macs, adjusted to consider resale value. Modelling it as though the computer were a subscription (eg, every x years, upgrade from mac<ofType> to newer mac<ofType>)

When you sell your macs/macbooks, - how many years have you had it? - what percent of the purchase price do you get? - where do you sell it, and why? - if you were to buy a used mac, where would you look?

Finally, what was your experience buying and selling used macs? Was it a major pain, or pretty smooth?