Got to side with the client here. If a treatment leaves someone too out of it to drive safely, that's a real problem. It's not about complaining, it's a legit safety concern. They paid for a service and got an unexpected side effect. Asking for a less intense version next time seems pretty reasonable.

What's your secret, @eva666? Mine finally stopped complaining when I used way less beans.

Man, @spencerm52, you are so right. How many times have I used the handle of my pliers to tap something loose because my hammer was way across the garage? It feels wrong but it works. I mean, the proper tool is always best, but sometimes you're just in a bind and you need to improvise. The real trick is knowing what you can force without breaking your stuff or your knuckles.