If it's too good to be true it probably is.
It's most likely double points on the purchase itself. The 800 points itself is a promotion.
So you'd get 100RZP instead of 50.
In a sense this is true. But it's also up to the retailers to protect consumers by issuing limits. If anyone is able to clear out a store, there's something wrong with the retailer's.
For example, if DS3s are on sale, there is no reason for someone to buy 20. 5 I can understand. 10 or 20 is...
That's exactly what I use, Shopbot. I decide on a video card and monitor prices until I find something great and price match it with NCIX.
I also read RFD.
Legally it's not wrong at all. Ethically, it's debatable.
Bottom line is their system structures the contract that way. That's not the customer's fault.