However, there's a mention on SR's forums that if you use a coupon/code NOT mentioned on her link, that the retailer can use that to not pay SR and therefore you won't get the SR credit.
That's what did it for me with buycostumes.com, even though it was a code that WAS on her link the day before (I didn't know about the restriction on codes before I did it). In my case the savings from the code was FAR more than the percent I would have gotten back, so it was worth it, but that might not necessarily be so in all cases.
Anyway, it's worth knowing ahead of time.