If you're looking at a door buster type deal check to see if there is an advertised model number on the tv then see do a Google search to see if it has been sold for a while or if no one has ever sold it before.
If there is little information on it dating back in time then there's a good chance it was made specifically for black Friday. Those tvs are generally made with cheaper parts and the MSRPs are inflated to make the deal look better.
All of this doesn't mean you shouldn't get it, just that some deals aren't as good as they appear.
One tip for looking up price history is to use sites like camelcamelcamel.com where you can plug in the price of an item from amazon and see historical pricing in graph form to see how today's price compares to the past