I have had Dawn till Dusk out to my house twice. The first problem was a noisy compressor; the other time, the outside unit appeared to be iced up. Both cases were false alarms. I paid just a service charge each time. Neither time did Dawn till Dusk try to sell me anything more. They could certainly have done so.
These guys are honest and very nice. They are not on a commission, so they have no reason to stick you.
The A/C business has a shaky reputation. Why go with someone you know nothing about? Given Dawn till Dusk's high Yelp ratings (and my experience), I don't think you can go wrong with them.