The proven method is to allow tipping.
I can assure that is not the case. I would love to know what the secret is to getting people to show an ounce of enthusiasm. A family member has a bakery and getting the front of house to engage with the customer at all is like pulling teeth, and this is an above-minimum-wage job with tips. They aren't on "commission" (it's been tried) but their tips are directly influenced by the ticket price (obviously).
The opposite - silence and stares - is uncanny, and has gotten much more common in the past 10 years. Everyone notices, and it brings down the vibe.
That doesn't mean forcing your workers to do X Y Z. What it means, IMO, is hiring workers who are pleasant. That would require a pay raise though, because you can't be picky at 10 bucks an hour.
On the other hand, I don't think I've ever received exceptional service in that situation either. I'm not sure what that would even look like. Beyond some eye contact and a friendly tone, what is the tip supposed to incentivize?
I second-guess it not from losing money, but by tipping, I may be incentivizing this low wage. I.e. I don't like the idea of tipping, but it's an easy way to contribute back to people who are getting hosed by our system.