It would be really nice to be able to either more clearly see a "summary" type listing of the products that each seller offers and not just the typical drop down list. The reason I mention this is if you use a lot of inventory control, updating your inventory can be a real pain. Or just double checking your inventory for that matter.
Maybe a possible solution would be at the very minimum to be able to download your product database in a csv or something similar. At least then you can see a broader picture of your products. Better yet would be the availability to save your csv and upload it back to the server after you have made changes.