using a utility transfer switch

[Charles V Tollefsen]

First off I am not an electrician, but before I call one I want to know if this is even a thing people do.  Here is the scenario: I own a duplex home with two electrical services, one for each unit.  I have a detached garage that has power attached to unit one's service panel.  The tenant who rents the garage lives in the other unit (Unit two).  Can I take the garage circuit off unit ones panel, put it in a sub panel and use a utility transfer switch to pick which service panel should feed it power?  Does anyone have a setup like this?  Wondering if there is a better or different way to essentially move the electricity usage from one tenant to the other. Thanks!