If a frame is damaged, in any way (dent, bent, rusted, cracked, etc.) I will buy the bike for the component group only. I don't have any interest in a damaged frame set. That said, as a rider, that dent is a non-issue in my mind. If the price is right and the bike fits, buy it and ride it, ensuring first that it is road worthy and safe to ride.
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"98% of the bikes I buy are projects".