I've posted several of my craigslist scores here in the past 2 or 3 years... two most notable purchases were a Leinbach post hole digger (not much wear on it) for $220 a couple years ago, then last year a 5ft Ro-Cut bush hog (nice shape but missing the front half of the PTO shaft) along with a TSC 5ft box blade (very nice shape but missing three rippers) for $400 from the same seller. That's for the pair, not each!!! Have scored some other deals too, such as a rusty but nice, heavy duty pond scoop made by A&B Eagle Line for $90. That one sold new for around $450! I wound up trading it for another attachment though.
I have dabbled at buying and selling a good many attachments over the years and enjoy doing it, and have made some money from it too. For example, I turned around and sold the post hole digger, the bush hog, and the box blade I mentioned above (because I already had those pieces of equipment) and made about $400. At the same time, it lets you try other pieces of equipment basically for free. If you buy good used equipment at the right price, it generally won't lose any value, as long as you don't damage it.
The thing about scoring on craigslist is you need to be on it a lot, use the search function if you are looking for a specific piece of equipment, be willing to travel a few miles, and have the cash in your pocket ready to go at a moments notice when those good deals pop up. A little luck doesn't hurt, either!