Why not increase your prices and target larger customers then?
Even if it had worked out, it still really wasn't worth it to increase revenues by $9k unless I was closing this sized deal at least monthly.
If the service is worth 150k a year, you could of sold it for 75k. Then it becomes possible to hire someone else to handle the day to day.
I think you made the right choice, having 10$ a month clients who expect hours of support per month isn't practical.