in CL you don't think about posting, but your ad will be removed by other sellers with higher price (happened to my nexus one when i tried to sell) and buried in a couple hours. and expire in a couple days. And then, the READER has to put in all the time the writers didn't put.

on other sites, you waste some time to write, but you can be sure you will not be removed without reason, the ad last longer, and the buyer can get there quickly.