It's cool that these games are included, but they often clog search results and they're almost never what I'm looking for. For example, if you search "Mario GBA" you get 29 results, 10 of which are Not For Resale titles. That's over 1/3!  Maybe give the option to filter them like is currently done with region. A little option that says "Include Not For Resale Titles" and let people pick. 

i have a bunch of these and this would be really cool because its a part of video game history

Just started a collection of Nintendo power and would like to be able to mark with or without poster. 

Exports are always in USD.  Let users export prices in their preferred currency

Can we add variants? Some of the Xbox Platinum Hits are very rare, such as 50 Cent: Bulletproof and command a higher price than the black label version. It also helps with the collection side of things to see what variants I need.

I would like to be able to sort my collection by system, then alphabetically if possible. 

Maybe a secondary sort field is possible, so you could sort by system, then by price, for example.

Search for items in a particular users game collection or games for sale.  If I'm looking at a game collection for a user, sometimes I want to see if I have a particular game.

Keep track of demos for games.  PS1, PS2, and PS3 have lots of demos.  It would be nice to know the values and be able to add them to my collection.