Background
Davin was always too smart for his own good. His family wanted him to study medicine, but he could not get the funding. He managed to win some of it by using statistics for an edge at gambling, enough that he could get by with that and an enlisting bonus through the military, but this gave him a taste for gambling.
Soon his luck ran out and his debts piled up, leading to him selling off excess and expired medication he didn't think would be noticed, and taking some credits for off-the-books treatment, this lead to him being dishonourably discharged.
He found his way to this squad with some favours to and from people he knew and trusted. He is a strong medic when his heart is in it, but he still deals with his obsession for credits.
Motivation
He learned the hard way that many people are not lucky enough to have a near infinite supply of medical equipment and easy access to Bacta tanks, so he strives to make up for his earlier ignorance by ensuring he will do his best to treat injured people in his care and never be frivolous with the medical supplies that he has.