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.

I use the SportsCardsPro API (/api/product) and would like to request one addition: sales volume broken out by grade, matching the grades the price fields already cover.

Today the API returns a single product-wide sales-volume, while prices are returned per grade — ungraded, PSA 9, PSA 9.5, PSA 10, BGS 10 and so on. That makes the volume figure impossible to attach to the price it sits next to. A product reporting 90 sales might be 84 ungraded, 4 in PSA 9 and 2 in PSA 10, and the API gives no way to tell.

Something like this would fully solve it:

"sales-volume": 90,"sales-volume-by-grade": {  "ungraded": 84,  "psa-9": 4,  "psa-9.5": 0,  "psa-10": 2,  "bgs-10": 0}

The M64 just came out and the Chromatic has been out for a year or so now, and both have not just their own console hardware, but their own exclusive games.