The last time we brought our old Subaru in they sa...

The last time we brought our old Subaru in they said they had fixed an issue where the car would die spontaneously without warning. What they did however did not fix the problem. We had them check it again and they told us something to the effect of, "We now know what the issue is. The problem you described we weren't able to reproduce the last time you brought it in, but now we see what you're talking about." We knew the car was old and was going to have issues. What upset us is that they "fixed" the issue and charged us to "fix" it without even spending the time to reproduce the problem and accurately diagnose the issue. I understand that there are a lot of things that can go wrong with a car, however when I bring it in to a shop to get fixed, I expect them keep the car for however long is necessary to see what the real issue is. I don't want to pay for guess work.