I hope you got a written estimate. Here's why,

A few of these things Air filter/drive belts seem like a good price but here's the rub. Anybody that quotes me $300.00 (in writing) for a job and turns around and charges me $700.00 would be subject me to a great deal of consternation, and would prompt me to discuss the many reasons why $300.00 is all they would be getting as payment.

Then i would find another repair shop.

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"What you hear in a great jazz band is the sound of democracy. “The jazz band works best when participation is shaped by intelligent communication.”
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