Checkoutmycards.Com

This is a website in which you can check out people’s sports and nonsports cards. Most of the time, you can buy them, too. Full disclosure: I am user joelshitshow, and I have tens of thousands of cards on the site for sale.
The way it works is that people send in their trading cards (but not the gum), and COMC takes care of the rest. So all the cards you see on the site? They are right there in Redmond, although I think you can only shop on their site. I dunno that you could visit them in person and expect to paw through some monster boxes of stuff.
If you have used sportlots, the big difference is that you can see the exact card you are buying, because COMC scans the front and back of every individual card. The other advantage is that you pay only one shipping fee, no matter how many sellers you buy from, because the cards all ship at once from the same place.
As you can imagine, the site is taking off and growing like gangbusters, so there are issues with slow email response time (but you can always call them during business hours and speak to a real person) and slow website performance, but they’re working on it. A victim of their own success? I’d say so.