Is buying a car for "less than invoice" a good deal?

Or is it a gimmick used by dealers to make you think you got a good deal? If they actually show you the "invoice" is that REALLY their price or is this just something thats a negotiation tactic? If MSRP is 26,200 and the invoice is 24,900 that means the dealers profit would only be 1300 on the car, which I find hard to believe. Especially if theyre offering a 1,000 cash allowance, which brings original MSRP down to 25,200 which is only a $400 difference between their supposed "invoice" and the net MSRP. Thoughts?