Precision Tune Ruined my engine. Beltsville, Maryland

Today, I brought my 1995 Mazda Millenia S to Precision Tune for a tune-up at around 2pm. The car was running great, except for a check engine light which was on steady. Precision Tune mentioned they would complete the job by the end of the day.  

They did not get my car into the shop until 5pm, and then called me at around 5:30 pm to inform me that the spark plug boots were covered in oil and were faulty.  They mentioned each boot would cost $30, and with my six-cylinder car, that amounts to $180 plus labor.

What was odd at first, is that I had read in numerous auto repair forums, that to change the spark plugs on my car takes approximately 3 to 5 hours, or more.  The rear bank of spark plugs is the most time consuming and difficult, and takes about 2 to 4 hours.

Precision said they took the spark plug boots off the rear bank in less than 15 minutes! I told them I did not want the new spark plug boots, and to put the old ones back on, and I would pay them for their time to do that.

They mentioned that the car may not start or work properly after doing that. Also, they said the spark plugs were never changed, but I told them the spark plugs were changed about 40,000 miles ago, and then they said, "We have never changed your spark plugs." After they put the boots back on, the car was running extremely rough, the check engine light was flashing, and smoke was coming from the engine.

Furthermore, when I asked the customer service person at the desk at Precision Tune Beltsville why did they did not inform me that the spark plugs might be damaged beforehand, and might cost over $180, he did not respond. I feel I was taken advantage of by Precision Tune they might have engaged in deceptive business practices.