well i at least figure to get something from what I paid. he diagnosed nothing. thats like a carpet cleaner coming to my house to give me a quote and telling me that its too dirty to clean and i owe him for looking at my carpet.
I assume there was some paperwork involved in all of this? If so, all good mechanics/repair shops will have their labor/diagnostics charges listed. Check it out. Now if you went to him and said "I need my alternator replaced", then he did what you asked and has a right to collect his labor costs. If you went and said "I have a problem with my charging system, can you check it out for me?" he should have been up front and told you what the diagnostic/labor charge was going to be. If he didn't then that's a problem. especially if you signed a work order. And if you did, take what you got and be glad he didn't bill you $1000. Cause you won't win that battle in court.