The conventional way to scam dell is waiting for some mistake on their discount system. For instance, when they mistakenly offer a, say, $400 off coupon while a previously reduced price on the same system did not expire it. Such overlaps may exist for a few hours, resulting in an unintended low price. Some of my friends were able to get $1000 systems for $400 this way. Check out fatwallet's forums. There are many instances of this happening.
Of course, this is not so much of a scam as a mistake on Dell's part.