You are being too obtuse in your definition of what selling mufflers does to the price of the stock.
Of course selling LOTS of muffler affects the stock price.
It does so in a short term way when they put out a Press Release indicating the volume of sales realized (and this time lets hope they are truthful and abstain from the triple digit growth BS).
The share price will react in a long term manner when those increased sales are translated into EPS as evidenced by the audited financials.
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