Can heuristic information processing affect important product markets? Analyzing over 22 million wholesale used-car transactions, we find evidence of left-digit bias in the processing of odometer values, whereby individuals focus on the number's leftmost digits. The bias leads to discontinuous drops in sale prices at 10,000-mile odometer thresholds, along with smaller drops at 1,000-mile thresholds. These findings reveal that information-processing heuristics matter even in markets with large stakes and easily observed information. We model left-digit bias in an inattention framework and structurally estimate the inattention parameter. Empirical patterns suggest the results are driven by final customers rather than professional agents.