Generally, "game knows game." Publishers know of each other. Editors know of each other. Art directors know of each other. That's the reason anonymous tear sheets don't really mean anything to them. They can pretty much sniff out what's been paid for and what hasn't.
There is a way to make it public displays work for portraits, and I do it, but just as with the case of charities, I pick them--for my own purposes--not the other way around. My displays are "free"--for public display in the specific places where my niche market goes to spend money.




