One other thing I would like to propose is a guideline that the seller should give some indication of what he/she is selling in the thread title.
The majority of people already do this, but these seem to be some gene-deficients who continually list with "High-Grade Books for Sale!" and "Lots of New Slabs" useless titles, and when you click on them you find a ton of off-the-shelf Moderns or esoteric nudies.
If you're selling Moderns, then use Moderns in the title, the same with Gold, Silver and Bronze. Selling a lot of Indies or Adult books? Put it in the title. Creating an all-encompassing sales thread with multiple eras? Then post "GA/SA/MA" (or similar) in the title.
If you're selling quality books or slabs, then outlining what is for sale is just good business. Life is too short to look at every single book posted here and I use thread titles to whittle it down.
For those selling *spoon*, I realize many use generic non-titles on purpose, as they want want to fool as many people as possible, but that's another reason to update the Guidelines.