Well, that's an easy one.
In 2004, we developed a new college admissions class we were really excited about. We spent $10,000 to 1) purchase a mailing list, 2) design expensive brochures, 3) drop a direct mailing, and 4) build a storefront for our website so people could enroll online. 9 people signed up for the class (at $295 a piece). You don't need an MBA to do that math and realize that we made a huge marketing mistake.
The class was (and still is) a great product. The mistake we made was thinking we could buy peoples' attention with traditional marketing methods (and waging a $10,000 bet it would work). That's the most expensive–and least effective–way to generate interest in your counseling services. Very few people will see an ad or receive a piece of mail and decide to buy college counseling because of it.
Tough lesson learned: You can't buy an audience's interest.
Knowing what I know now, I would have first offered the class at a reduced rate to friends of our existing customers, something they could "give" to people to get a little taste of what we do at Collegewise. I would have offered it on campus at the high schools where we had good relationships with the counselors, split the profits with the school (so we'd both win), and maybe let them choose 1-2 deserving kids to attend on scholarship. I would have done the same thing with the test prep companies we enjoy a good relationship with, and leveraged their permission by having them announce it to their customers.
So yes, it was a $10,000 mistake, one I'll be careful not to make again.