you dont have expansion modules

It is a hassle, especially if you have many items, to know whether your listed prices are in line with others who might also be selling the same game(s). An example is Amazon's "Match lowest Price" option for sellers. It keeps prices in check while also helping to curb artificially inflating game values.

We need to be able to communicate directly through the website. The e-mail messaging system gets lost with the hundreds of other e-mails I recieve. Plus it'd be a lot easier to organize and go through the messages and whatnot

It would be useful to be able to view the marketplace through the mobile app. I would especially be interested in features similar to the eBay mobile app. Mainly ones, such as getting a notification on my phone when an item sells. This would allow me to potentially ship sold items more quickly.

Let me see only listings with actual photos of the item instead of stock photos.

Your pricing on some rare games makes no sense - for instance Bang-O NEW sealed copy is less than a loose price. Obviously this makes no sense and your system should recognize this. Don't use any price would be better - although I found examples offered on games on Amazon. This is a bad flaw, and really hurts the credability of your site.

When I search Charizard, or pokemon base set, I want to quickly see what cards I do not have by filtering out the ones I do have.  Bonus feature request is increase the cap of displayed cards from 200 or allow pages so that I can see more than just 200

For silver and gold coins, it would be nice to have a running total of how many ounces of silver and gold you have in total for the entire collection

Would be helpful to have the option to add raw autographed cards. For example a raw 1987 Topps Barry Bonds card is worth $1 while an autographed raw version of the 1987 Topps Barry Bonds card would be worth close to $200