I own three. One brick and mortar business and two internet businesses. The shop is a challenge--a hell of a lot of responsibility. The overhead adn paperwork among additional taxes, fee, etc. make it very frustrating and it is a HUGE commitment--you are married to the business. I have owned and worked in my shop for 11 years.
The internet ones are different. Selling the restored bikes is random and fun. Selling parts can be pretty time consuming but the income is reasonably stable.