Have not had a problem with Yellow Checker Cab the 4, 5 times I've called. Most of these times are me trying to catch a plane at Willard (I believe they charge a standard of 13 per person).
I have had the cab show up exactly when I called to ask when they were arriving (so about 2-3 minutes late). And the dispatch on the line doesn't always have the most welcoming customer services you will receive; however,I have had good experiences with them, getting me to my destinations.
They are definitely reliable the times I've called them, and I will continue using their service until my experiences says otherwise.