Honest buyers need a fair size comp to help sell their ideas but images are so inexpensive I'm not sure why they can't just buy them and if they don't end up using them they are not out that much. Institutional buyers buy many images so they may want to try before they buy. Dishonest people will find a way to snag an image they want either here or via other sources like google images. You hate to punish the honest ones. It would be nice to know how many comps are turned into purchases but that is impossible to measure. At this point I don't think the comps are too big, they serve a purpose albeit sometimes a purpose that is ultimately a ripoff.