Bad Bad Service Experience ever

My service experience for my car wth Gariep Motors was always a bad experience ever sins d car was no longer under warranty/motor plan. My latest worst experience was yesterday after I towed my car last week wednesday to the dealership warning light that pop timeously showing coolant level low..They done the diagnostic (so they reported) an give me a list of findings escalating to an amount of 18000r.I informed them not to continue with what the list of defaults and i will just pay d diagnostic..Yesterday when i went to collect the car I paid for the diagnostic (+- 1000r) requested the print of the diagnostic...to my surprise there was None...I demanded and was 1st told they not allowed to give me a print..I thn requested to see the workshop manager who by then apperantly was out of town.Then i learned/was told that the technician who worked on my car is on leave n no one know the wherabouts of the diagnostic print.I was still adament to get a printout wheron alot of verbal promises was been made of follow ups when d workshop manager is back...my conclusion on matter that was how did the technician get to the findings without a diagnostic test...the foreman also didnt signed off on the job card but quotation was already been genersted. Now the big Q is how customers go on a daily basis thru such ordeal..what if i had agreed tht they continue wth what the believed was d problem yet they cant proved the diagnostic...