Andar + gerund is a kind of progressive construction, just like estar + gerund (estaba cerrando un negocio). They are close in meaning but not identical. In English you would probably translate both using to be + -ing.
Andaba cerrando un negocio means something like "I was trying to close a deal" or "I was in the (somewhat convoluted or protracted or interrupted) process of closing a deal". Andar works like an auxiliary verb (though you won't find it as such in a basic grammar textbook); note, it has nothing to do with andar in its "to walk" meaning (although it doesn't exclude the possibility that the action involves walking or moving around, of course).
According to the Nueva Gramática de la Lengua Española (NGLE), andar + gerund is a "frequentative periphrasis". It says the phrase does not imply that the action or process is finished, and that it describes "situations that develop with interruptions or intermittently". (This is all on p. 2198 and 2199 of the NGLE, which is unfortunately not accessible directly, but if you're interested, you can go to the search page and look for the phrase "andar haciendo algo".)