Are we talking in terms of good marketing that wasn't sufficient to back a bad product, or bad marketing which killed a good product?
If it's the former there are plenty of examples. New Coke is probably the best.
For the latter it's a little more difficult, mostly because bad marketing usually means the product was made forgettable. Hybrid cars are about as close as I can get. And if you're a Reno local there's an ad that used to run on the radio for a paycheck/title loan place which featured the line "if your only gambling problem is not having enough money...."