Right, that's not the way to run a proper business. I have spent enough time to burn through a tank of fuel in a Duramax plus some more fuel (that I didn't bill for) and only billed a couple hours to figure out it was a rubbed wire. I was taught that troubleshooting and finding out what is good is worth as much money as finding out what is bad, but there is a limit. If I am chasing the wrong rabbit because of my ignorance or a mistake, the customer doesn't pay for that.
And remember that there are times when replacing a part that doesn't fix the problem is the proper thing to do. One example is a no start with no glow plug light. Most old timers here would look at the relay 109 and if they see a black one, they would replace it. But what if there was a wiring issue? To me, it's perfectly reasonable to charge to replace that relay because the black one is a known piece of garbage.
Of course none of what I'm rambling about has to do with your situation, but I mention it just to remind folks that there is more going on than they see. And we are all human and can make a mistake be it not communicating properly, or being so busy, they miss a vital bit of information that costs a customer time. They true tale of what kind of business they are is I how they handle it. I just went through something like this from the customer side. An assembly I needed was held up because they missed something I told them. When talking to them on the phone, I could hear the regret and apology in their voice without then even saying the words, "I'm sorry". And they gave me a few extra parts for free. It cost me half a day, but I would do business with them again because of how they handled it.
Hopefully you can get them to get to the point that you are neutral about your opinion of them, which would be a long ways up from where you are now. Unfortunately, after reading those reviews, I doubt that will happen.