Not sure what PWCC takes in feeds but they have a lot of listings posted on eBay. You would be paying more in fees.
However, for the extreme high-end a lot of people do not want to deal with eBay and would rather deal with PWCC. I believe in some instances PWCC uses other platforms like eBay to get 'more eyes' on the listing.
I have never sold anything more than $1,200 CAD and that was through eBay. My cousin has a card worth about $4,500 but he will only move it in person at the Toronto Expo.