Here's the thing about craigslist ads. People aren't listing for fair market, they're listing to sell and make decent profit, with the expectation that the potential buyers will try to haggle a bit. That's just how private sales work.
Even in places like Mexico, Japan, and an extremely large portion of the world (including many Euro countries for that matter), almost have bartering available everywhere. In Mexico things listed for 200 pesos (20$) can be bought for as low as 20 pesos, even in the stores. I would routinely purchase bottles of tequila that were listed in stores @ 400 pesos for a measly 50 pesos.
In Italy, my friends bartered down hand bags by being flirty with the store staff, to nearly half price. Japan even has a word that is commonly used, meaning something along the lines of "give me a fair deal".
The point is, it's not uncommon to go looking for deals, so list high because someone's always going to be low-balling you. On the flip side, low-ball people for stuff that they're selling, you just never know what they've actually invested, and what they'll accept for price.
I met someone on these forums in real life, by what I felt was low-balling an already low price on an asteroids cocktail (*AHEM* burt *COUGH*). Cocktail was listed for 250$, I shot him a low-ball deal, lo and behold he was all over it like a fat kid on a cupcake!

I met a great guy in the process that's been an indispensable resource. On the negative side, he got me hooked on pins. Asshole.