About 8 years ago, we've built a SAAS for purchasing material for companies using auctions. The idea was that if it will be super easy for companies to do reverse auctions and use them to buy material they will save a lot of money (proven concept in those who actually used it).
But what we learned after some time was it didn't matter. Because people in the companies responsible for buying material didn't really care for how much they buy it. They care that they call their favourite supplier have a nice chat and then order whatever they need. And those suppliers throw some "gifts/rewards" to the package here and there. And without appraisal of those people the business owner never said yes.
The thing was that those people who effectively decided if they will use it or not didn't benefited from it at all.
We haven't lost so much money on that, but the lesson learned was huge.