I'm fairly certain scaring people into buying something is illegal. I work at an oil change/small repair shop that's privately owned. You do what you gotta do to up sell a product but you don't scare people into buying stuff or lie about it. My general rule of thumb is, if I won't use it, I won't sell it. Like that magical engine leak sealing crap and radiator sealer crap. If its leaking, fix it right! Synthetic oil is just oil that is man-made. It does the same thing as conventional oil only a bit better. its not thinner and makes leaks like people say (if it was thinner it would be a different viscosity) it doesn't cause leaks (if it leaks you had a leak before that was clogged with dirt that conventional didn't clean out and the better cleaning synthetic oil cleaned) but I would seriously give that guy a piece of my mind if I were you.