My experience has been a 90% success rate with calling ahead to schedule a pickup (meaning 90% of the time they show up when theys say they will). This is far better than some other companies and I've been really happy with the service. You can also find Barwood taxis at hotel taxi stands in downtown Bethesda. I think MD taxi rates are standard, and they are posted on the window. If you want to pay with a credit card, tell the dispatcher when you all, or the driver before you get in if you're at a taxi stand. Not all of them will take credit cards.
I've had one bad experience- I needed to go out to the main Bethesda post office once and got a cab at the Hyatt hotel. I explained to the driver that I needed to go to and spend 10 minutes max in the post office to pick up a package, and then come back to the hotel. He agreed to this, but got another call on our way out. He tried to leave me at the post office, which is in the middle of an industrial park!! I asked him, "how am I going to go get back?" His respose- "there's a bus stop over there." I really couldn't believe it!!!! I told him no way, and he did end up staying...
But, otherwise I've had some wonderful drivers and great experience with Barwood.