For the last comment about "at Staples stores", all of their rebates say this and they honor them. They really have to because the phrase is ambiguous. It could mean, "must be at our brick and mortar stores", or it could mean "from Staples, not anyone else". Well, thanks to the law, the latter interpretation is the only one that will fly, especially when you consider that the rebate coupon appears right on-line. To argue otherwise would mean Staples would have to argue that those coupons that they clearly put on their web pages which clearly lead everyone to believe that they apply to on-line purchases, are in fact only for BM stores... No way my friends. They would never try to argue this point, because its a sure loser and could land people in jail for fraud. Staples is putting their rebates on-line for the express reason of customers using them for on-line purchases, not some ill-conceived conspiracy.
Now the other point about combination of offers, that one gives Staples far more wiggle room. If they really wanted to fight you on that point, they would at least have a decent argument. However, I think that many of these rebates are in fact Manufacturers' rebates and if so Staples will get paid in full for them, so you should too. It doesn't matter how much you paid Staples, the money is eventually coming from the Manufacturer.