Sounds like a minor usability problem has cost you a potential customer. The question is how many other customers have had the same problem but not bothered to write blog posts.

Relying on tooltips is probably a bad idea. Maybe change the button text to 'X seats at this price'. Don't make me think. :-)

On the bright side, be thankful for the good user feedback. I wish everyone who stopped using my product wrote a blog post.