Each Business owner can have more than one Listing / Business per Account. The businesses or listings he owns will appear in Account Dashboard in the following manner:
Setting Maximum Number of Listings Per User
As admin you can set the maximum number of Listing per user, by visiting Toolkit Options > Business Settings > Maximum allowed Businesses per user option.
Setting Maximum Number of Listings Per User in Subscription Levels
If Subscription is ON, and your website is based on subscription to allow your users to create listings, then while creating a memebrship level, you can set the maximum allowed listings per user. Note that the maximum of this maximum is set by the option set above.