1: If you have a phone with internet access, or an mp3 player with wifi, and there is a wifi hotspot, go to your favourite retailers and look for it. If it is a better price (factoring in shipping), definitely go for it.
2: Ask vendors about availability, see if it is indeed the last in stock
3: check to make sure nothing is missing or damaged.
4: If all of this is true, don't go anywhere else in the room, buy that shit.
Also sometimes they will sell things for way low at the end of Sunday, especially large items. It's a scramble, and you should watch your finances, but you will regret things you don't do more than things you actually do, I think.