Best Buy sales people aren't on commission. As a part of the price match, they will require both the ad and will call the other store to verify that they have them in stock.
Considering how busy the holiday times are, any associate will likely send you up to customer service for the price match, at which point they will want to know the pertinent information about it and will call Walmart and/or Meijer to find out if they have them in stock. Now if you're lucky, they'll get tired of waiting to get through to those stores, and if you're nice they might do it.
But keep this in mind. People try this at retail stores all the time. Employees know that customers don't just come in and want a price match for no reason, that means that either the store is out of stock of them, or really far away (and in most cases the "local market"comes in to play, for example when I worked on the West Coast of FL, we would NOT price match things from the Miami area, which in some cases were cheaper. We also didn't price match competitors that were not anywhere nearby us (ie if there was no Meijer within 100miles, we wouldn't price match their in store stuff).
Anyways, you might get lucky. But next time remember to shop earlier.