Give out serial number when selling?

That is the easiest way of a buyer getting all the specs on the machine that most sellers neglect.

If in doubt you can run your own SN and give out the associated information as an alternative:

https://everymac.com/ultimate-mac-lookup/

also important for you:

What to do before you sell or give away your Mac - Apple Support

Kebarlow wrote:

My son is selling his MacBook Pro and someone wants to know the serial number so he can look it up. My son feels this is suspicious. I don't know enough about computers to know if it's a problem to give it to a potential buyer or not. So, you are saying it's ok to give out to a potential buyer? (Obviously, not just post it openly anywhere.)

There isn't a whole lot that anyone can do with it. It would be like asking for a license plate number before buying a car, where one could check to see if the title is clear.

You're not supposed to post it here, but I wouldn't worry about it if I were selling one. The potential buyer could check the warranty/AppleCare status as well as have an assurance that it's real item.

it can be used here to validate the system

Check Your Service and Support Coverage - Apple Support