That's horrible advice.
Make sure to meet in a public place to test out the computer. Starbucks is good, but even better is an Apple Store. You can set up a Genius Bar appointment in advance to have them do diagnostics on the computer. Make sure to check:
- That there is no firmware password (or you can set one yourself) - you want full control of the hardware.
- That it is not stolen (based on serial number, and checking with Apple to see proof of purchase). If the computer is already "second hand" (i.e. the person you are buying from got it from someone else), don't get it no matter how good the price is.
- That it is in good working order. This means that it will have the same specs as what the seller claims, and that it works well. You may want to run diagnostic tests such as from Tech Tools Pro to see the state of the SSD, memory, screen, etc.
If you do end up getting the computer, make sure you get full documentation of the sale (a real receipt with date, purchase price, seller's information - driver's license, date of birth, address, etc.) as well as the seller's documentation (their receipt from when they purchased it from Apple).