Careful doing that on craigslist. There have been more then one situation where someone got cockpunched for scalping a video game system on there and ended up -1 Wii/PS3/360 and minus purchase price of said system.
I don't wish ill on anyone, but I wouldn't feel bad for someone manipulating the system to have this happen.
You aren't doing a service to a person by buying the system and then selling it for more then your cost. You are a parasite when it all boils down to it. Sure, Person X may buy the system from you for $80 above the MSRP of the machine, but you took the opportunity away from person Y for buying it at $250 at the store if they do not have anymore left. Now if Person Y wants to get a Wii, they will either have to pay your higher fee for said Wii, or wait longer until they can find one at a store for the $250.
What if a person wants to buy a Wii for their kids for Xmas. And it would make them so happy if they got one. But poor mom is single and works 60 hours a week at 2 jobs just to make ends meet. Also poor mom has been saving up all year for the wii for her kids and can only justify spending the $250 plus tax for the console as money is tight. So now mom has a choice to make. Does she pay the douchebag selling a Wii on eBay or Craigslist an extra $80+ for the wii and have to cut back on groceries so her kids are happy and have the game system to play while their tummies are rumbling. Or does she buy them a Vii since that is all she can find in a store and the kids are disappointed and broken hearted for getting a cheap chinese knock off that has crappy games? Or does she decide to wait and on xmas morning the kids only have one present to open which is a picture of a Wii that you are holding in your eBay/craigslist ad and saying that she needs to save more money to buy it from a douchebag.
Sounds pretty parasitic to me. But if you can sleep at night knowing that because of people doing what you are doing won't have the opportunity to play with a Wii while you count your few bucks here and there.
There are better ways that you can make even larger amounts of money and I talked about it earlier in this thread, but it's something that takes skill, time, patience, and you aren't considered a douchebag because you found a great deal on something else that isn't taking away from anyone.

Get your Portable ID!
My pokemon brings all the nerds to the yard. And they're like, "You wanna trade cards?" Damn right, I wanna trade cards. I'll trade this, but not my charizard.