We provide a money-back guarantee of compatibility on all items purchased from GALAXY as long as you include your Mac's serial number with your order.
Locate your Mac's serial number as follows:
MacBook/Pro/Air; Mac Mini: Underside of the computer by the regulatory markings.
iMac: Underneath the stand.
Mac Pro: Rear case (2006-2012); bottom surface (2013).
* FYI - if you have a working Mac you'll find the serial number when you select About This Mac from the Apple menu.