Trade in Macbook Pro with Ubuntu OS

Unless you reveal that it has Ubuntu installed (and possibly no Mac OS?), you would encounter problems with the buyer. If I was the buyer, I would insist on a full refund plus return shipping costs.

This is what you need to do before selling a Mac (and I have no clue how to uninstall Ubuntu):

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

Unless you follow all of that, your Apple ID will still be associated with the machine and I'd also return it for a full refund since I cannot do a thing with it (no access to app store, reinstalls, etc).

If using the Apple trade-in system, read the rules very carefully.

Does it say must have OS installed? or does it say must be working?

they may argue with only Ubuntu installed, it is not working properly.

Does it say must have OS installed? or does it say must be working?

Thanks for bringing that up; prompted me to check that out. And, according to the info here:

@ xin129:

https://www.apple.com/shop/trade-in

they reference the very same article used for selling a Mac:

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

which includes that you must erase the device and reinstall the OS.