Keep in mind that Amazon and eBay take roughly 8.5-10% of that. The laptop cooler does not add that much value to the laptop, so I wouldn't advertise it as such. The cooler is like an additional fifteen to twenty bucks on Amazon. Chances are, 99% of the time you will lose out on some of the money you paid for it, unless your buyer is a scammer, they're generous, or they just have no clue what they're buying.
You want more information on what to expect from Craigslist? Google Craigslist Buyer scam and add Paypal, Western Union, escrow, eBay escrow, etc., and prepare to lose faith in humanity.
EDIT: I would suggest keeping your ad here on the 'Temp. Scam rates are crazy low and only a handful have made scams in the past several years.
EDIT 2: Honestly, the way I'm reading it right now, it appears that you have never ever sold a thing online, and you have quite a ways to learn. It's not a bad thing, I'm merely looking out for you in a way. I'd suggest doing a lot of research and possibly pulling your listing, because for a newbie, you do not want to place high value commodities on the eMarket, simply because you aren't experienced enough yet to spot what a scammer can do. I've had some horrible stories happen back in my day, and I honestly feel at this time that you simply are not prepared to do this yet.