If you genuinely think the helmet doesn't work as it should, and that the salesperson caused that, I can see returning it. I just think it's hard to square that with a year's use.
And whether it's right or wrong doesn't depend on whether your Warren Buffet, or work at MacDonalds.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.