Aiya, both sellers and buyers got their own part to play, think it might be an issue on education.
First sellers, You need to post on your Title the object for sale, some brief descript would be desired (ie. WTS : MIK Ibanez RG350DX << Clear enough?). Putting the words, cheap, sale or wateva... dun actually have much effect (imho) cos people are just gonna run through the ads anyway if they're interested/looking.
Next, you'll need to state the price. (ie. Price : 500 (neg/)) This gives a clear gauge to the buyers whether or not they have the ability to hit anywhere close.
Contact info : Well, this can't be omitted now can it? (unless you just wanna be flooded by PMs, which is fine...) Adding in a contact and preference of method of contact (ie. Call me at 98765432 or SMS only [hey, I've got work, and I don't want you to call me in the middle of a board of director's meeting!!!]) reduces some unwanted troubles.
And pictures. This can't be under/overstated. Pictures are an important way of advertising your product. (Some people cream at pictures...) Any flaws or defects that can be taken, take 'em, and put it up to avoid excessive SMS/Calls flying about.
Well, there are other issues such as condition, history, and other comments that you might think is required, add 'em. You never know there might be people who don't like "gigged guitars" or what not.
Next, issue of buyers. Aiyo, with all the above added in, what else you want? Go through your own inner thoughts by yourself first, got idea already then call the seller larz... You think you free other people got no life meiz... Seller just wanna sell something, not entertain you leiz... We don't get paid (hmmm, well not on a monthly basis or commission wise) for selling you our stuff. If you really want the gear, but have some issues/difficulties, its the seller's prerogative to decide whether or not he shall entertain you, so don't go off lowballing or what not, its just irritating.
Wah, but once issue also not touched here leiz... What about the rising amount of people flying kite/fly airplane? Should we have a you must have at least insert number of posts, insert number of rep before you can buy stuff? This is getting out of hand, seeing the number of good buyers who genuinely have great prices for great gear up getting @$^#$%^... Hope my buyer doesn't fly too, gave him time allowance by reserving the guitar for him...
When I really need an item, I immediately call the guy for a quick deal... 
