Why not post a picture of your "for sale" item

Without pictures you loose potential buyers. If no picture only the person that really need the item will look at the ad. With pictures a lot of people that dont really need it but might buy anyway will look at the ad.
The "thats cool I want that" factor is important when selling stuff.
It's really basic marketing strategy, if a buyer can see the item he is a lot more willing to buy. I am not shure about the exact numbers but it is around 60% more likely to sell an item that has pictures in the ad than the same item without pictures.

As someone mentioned pictures can be manipulated and deceptiv, yes, but someone that posts that kind of pics will most likely not mention any hidden defects in the text either.