Companies cannot charge an increased restocking fee even if you buy, return, buy, return. If you're going to return and pay the 10% restocking fee and walk out with another MB I'd question why.
I would say to them that all you want is a straight exchange. No restocking fee should be applied because it's a straight exchange. If you were going to give the MB and walk out with a MBP, I would also say the fee should be waived. However, if you're going to return the MB for a refund then I would say they are within their right to charge the restocking fee. However, you may be able to tell them you'll take store credit in exchange for waiving the restocking fee. I did that. Now, had they already had the new Airs in stock I would have just told them to give me the Air, I pay the difference and they waive the restocking fee. The goal is to allow Apple to keep their cash as it was already realized and you walk out with the same or better machine.
Going back to your original question though, there is no legal right for a company to increase a restocking fee due to a second return. If there is suddenly some right then I'd like to see that posted in plain english on the receipt.
Well, I just returned it. The guys working at their so-called "Genius" bar were idiots. They probably felt better about themselves, because they thought I did not know what I was rambling on about ... 9C8C, 9C89 ....
They probably thought I was some half-informed dimwit trying to ac smart. But that's how it always is for me, even at the Apple Store. They rarely ever have answers for the questions I ask.
I feel great, having gotten back 90% of my money. Although I do feel bad about the restocking fee, but oh well.