Reviews.
I ask every customer for an honest review, good or bad, and nothing is offered for one. They are all on Google, where I can't choose which ones you see.
I am just opening, so the first review has not been written yet. Until then, the best reference is a conversation: ask me anything and judge the answer.
Not sure what it needs?
Tell me what the machine is doing. I reply with a price or a question, usually the same day.