If he customizes the machine, he cannot return it.
Yes he can, it'll be sold as refurb. In USA there's 10% restocking fee. When I was sending my iMac back and forth because of dead pixels the guy always asked do I want to return it, get another new iMac or other Apple product. He confirmed that yes, I can return it if I want
EDIT: Actually, you can't return it in states but in Finland you can, strange....
USA store:
Items that cannot be returned include:
Product that is custom configured to your specification
Finland store:
If you change your mind, you can return your Standard or Configured-to-Order hardware to us within 14 calendar days of delivery