Unless you buy a Macbook that a year or two old, the best you can do is 10-15% which is pretty underwhelming in my opinion.

If you do buy one that is over a year old, the discount can go up to 25%, which is a horrible deal for a computer that was released 1-2 years ago.

Personally, if I were going to buy a used model, I'd check out what's available locally on craigslist.