Bearing in mind that many artists appear for reduced fees at small venues, they no doubt rely on CD sales to help with recouping the 'lost' part of their fee, so I can't see a problem with putting them out - if I see CDs out for sale and I don't want to buy, I just ignore them.

Support artists frequently appear at venues for no fee at all, and have to stand their own travel costs, so in fact they are paying to appear. We're not made of money FFS, even those of us who work for a living and, given the high cost of travel, not to mention the time and effort that unpaid performers have put into appearing, a venue trying to dictate whether and when they can display their CD's would seem especially niggardly to me.