MacBook Air 13-inch year and model information

Current MacBook Aurs use M4 chips and are available wurh 13” and 15” screens. You can custom-order them with up to 32 GB of RAM. They are the first M-series MacBook Air models to be able to drive two external displays at the same time as the built-in screen

MacBook Air 13-inch and MacBook Air 15-inch - Apple

I presume you mean buy from a 3rd party, not from Apple or an Authorized Seller. Have the seller provide the serial number, then you can input that into the Apple Trade-In tool and it will provide the model details. For example, when I enter the serial number of my work Mac, it reports: MacBook Pro M1 Pro 10-Core CPU and 16-Core GPU 16" (Late 2021) 1TB SSD.

I understand the desire to save money by purchasing a secondhand Mac. But the only way to do that is if you can meet the seller in person, and have them boot the Mac to show the setup screen (either the scrolling, multilingual ‘hello’ or the select your region dialog).

Anything else and what you thought would be a less expensive Mac is more likely a very expensive paperweight, because it is subject to Activation Lock or managed by an MDM.

Don't. Buy a machine from Apple or an authorized retailer instead.