When I look for stuff on CL (I've been boat shopping in the Pittsburgh area for over a year now) I steer clear of posts without pictures. Honestly if the seller cannot be bothered to post a picture of whatever they are selling, they probably aren't 100% willing to sell or negotiate a fair price.
Sellers in general without pictures should be steered clear from, but I would guess that sellers with expensive things such as cars, boats, etc. have more reliability.