Branget, to me the big difference is not the seller audience, or the ease for running a sale, but the competition.
I list a book on ebay, and unless someone is looking for that exact book, it's never going to sell. Just to much chaff surrounding it. Ebay has 44k plus listings that come up when you search for "CGC". If you are trying to sell a book the only way it gets noticed is if someone has a search for that exact book, or if you start the listing off at .99 and get enough "lets try to win it cheap" interest.
Here a sales thread may be competing with at most another dozen active sales threads on a given day/night.
And the ratio of eyes to buyers is higher here (fewer eyes, but a high percentage are buyers) than on ebay (with millions of eyes, but very few buyers).
Sure there are a select group of people who comb all of ebay looking for under GPA deals, but the odds of getting eyes on your listing among the thousands of other comic listings is not as easy as listing here. Sure you get 800 views, but those views are far more likely to buy than the ebay views.