The wines have to cost $10 or less (Dallas prices, though I will make an exception if prices seem to be higher here) and be generally available. That means no store brands or private labels -- wines like Trader Joe's Two-buck Chuck, which are only sold at one retailer.
The final decisions are my own, and take into account what I think wine should be: varietally correct, balanced, and interesting enough to buy again. I taste most of the wines that make the Hall more than once, and regularly taste the wines with others.
Finally, I take suggestions and input from blog visitors and wine drinkers, people I know in the wine business, and other wine writers.