BUYING A SECONDHAND MACBOOK

Well first of all, make sure you completely trust the seller and website you are buying it from. Check every last detail of the listing before deciding to purchase it. You can buy a refurbished Mac from Apple here. It'll work just like new and can be discounted significantly. Otherwise, I'd personally recommend anything 2014 and newer. If you plan to do resource-heavy/graphics-intensive work, go with at least a 2016 MacBook Pro. If not, go for a 2015 or newer MacBook Air. The newer it is the longer it will last, and the longer it will receive support and software updates.

Hope this helps,

Fin

I'd recommend this place highly, you can even purchase a 2 year Warranty...

https://www.macofalltrades.com/?gclid=EAIaIQobChMI5L-I8oXo3wIVRR6tBh2ingBtEAAYASAAEgLvnfD_BwE

Most people would say a 2012 at least, others would say 2015 or newer, I'd say 2011.

Make sure that either it can have the RAM upgraded OR that it comes with at least 8GB of RAM if it can't be.

If you told us what you planned on doing with it & for how long, we might be more specific.

Lastly, make absolutely sure that the seller follows every step in this article, particularly erasing the entire disk and reinstalling the original OS as that is the only sure way to disassociate the device from the previous owner’s Apple ID.

That also applies to third party software which is not necessarily legally transferable.

https://support.apple.com/en-us/HT201065

Some options—

https://www.apple.com/shop/refurbished

https://eshop.macsales.com/configure-my-mac/macbook-pro

One consideration, it seems the 2012 non-retina MBP (the old work horse) is the end of the line for upgrading past the current macOS Mojave.

I wouldn't buy anything on this list: Vintage and obsolete products - Apple Support

The first tip would be to know what computer you are buying. You said you are buying a MacBook so be sure you know what a MacBook is. Don't let anyone sell you a MacBook Pro or MacBook Air if it is a MacBook you want.