Question for the forum... Please share your experiences and thoughts on third party upgrade events.  Guarantee or no guarantee???

I am exploring adding third party events to our established remarketing program, and looking for some experiences that other dealers may have had, and which companies they have utilized.  I am hoping for some cost structure and ROI expectations, as well as traffic assumptions.  Easy for the vendor to project, would love to hear the htoughts of those who have ventured down this road previously.

Thanks to all who respond, and Sell 'em all!!