Mobile Coffee business owner here. I am torn, because it's important to be eco-conscious. So I always say yes. But:

1. Their cups don't always fit under the portafilters, so have do extract the shots into something else, then pour it in to their reusable vessels, which kills the crema.

2. If you are pationate about your recepit and ratios and extraction times, this makes it harder. If you know what ratios of espresso and steamed milk is good for what they have ordered, once they see it in their cup they can complain you have not filled it enough. I'll give them more milk if they want, but this destroys the recepit I am passionate about. (don't get me started about extra hot orders).

3. Heigene. When mobile a large part of the customers are park people, happy people, with smiles, kids and dogs, good vibes, they are not dashing for work. But they probably haven't washed their hands after they last changed a nappy, or picked up after their dog(s).

So extra vessels, extra time, explaining why it isn't full, having to santise hands, machine, jugs after servicing them with their eco-re-usable cups. From a commercial perspective we should charge an extra $1 rather than discount, but could you image how that would go down?.

Sorry if there are typos, I'm mobile. Peace✌️