While profit sharing may work as an incentive for shift managers or store managers, in the absence of tips most baristas will expect some other immediate bonus pay, preferably based on a measurable metric that doesn't depend on factors beyond the barista's control, such as cost of goods sold, supply chain constraints, rent hikes, recessions, etc.
If you occasionally ask the customer in-app "how was your service today?" with a simple thumbs up/down option, and you associate the order's rating with the barista behind the counter, you can get a good metric on their interaction with customers. You'd probably want to use the median and not the mean in order to remove any outliers.
