Of course I would not buy something I can't see or evaluate. I know there are a lot of pictures that do not do a coin in hand justice, so you have to determine if the picture actually represents the coin or not. Dave
For slabbed coins with numeric grades from the top 4 TPG's, photo's should be required. For all others, photo's would be nice but again not required. If a person regularly sells on the For Sale forum, perhaps listing the forum names of folks you've transacted with would be helpful.
I don't believe they should be mandatory, but of course the effort that someone puts into the listing may very well reflect the response they get out of the listing. But, heck, what do I know; I've started a couple (two? three?) BST threads at CT and I don't recall selling anything listed in them.