1988 Ford Mercury Topaz: getting ripped off?

My apologies to the mods if this is an inappropriate post.

For a good while now my father's car had been messed up. It was dying at stops, and it would need to be restarted and given enough gas to get it going before it died again. If you drove it for a long enough time though this problem would lessen and eventually would cease. The car needed to be taken in but it was delayed for about 3-4 months (bad ya I know ) So I took it up to a repair shop, and of course it died at 3 different stop signs, and even died in the parking lot of the repair shop, where I had to restart it and park it. This was on a Monday. On Wednesday they called, said that a sensor was replaced/fixed and it would cost $172 (ripoff there too? Not sure). So I went up there, and when I got there the guy said he tried to call to say the head gasket blew, and to just keep the money. Well come to find out on Thursday (today) he said that the head gasket had blown *before* being taken up there. So I have to ask a few things here: (mind you i'm terrible with cars but this seems suspicious)

1. If it had blown, would I be even able to drive up there in the first place? The mechanic said it would be possible
2. Shouldn't a blown head gasket be pretty noticeable while driving?
3. They hooked up to a machine to check for problems. Would this machine be able to detect a blown head gasket? If so why would they call up *before* it runs a full analysis and give a price?
4. Don't they have to run the car to check out a problem like this in the first place?
5. My father had said 'ya but they're losing a $172', because they aren't charging and he's free to pick it up. This to me sounds a bit like sucking up to get out of the responsibility of a $500 repair that was their fault. I would think they'd have to be extra nice to do that, cause if it wasn't their fault in the first place I'd assume they'd just charge the $172 without fear of legal hassle.
6. In reference to #2, I had not noticed anything different the day I drove it up there compared to any other time driving it.

To me, this sounds like somebody in their shop blew the head gasket accidentally, and now the shop is trying to get out of it via playing nice guys and saying that it had been blown before it got there. Again, I'm terrible with cars, so any help on this would be much appreciated. Thanks

it's a 4-cylinder and as far as miles, I can't really give an exact answer since it's been awhile since i've checked