How can you distinguish tit-for-tat pricing designed to sustain “collusive” pricing from competitive pricing?

Suppose that you were trying to determine whether the leading firms in the automobile manufacturing industry are playing a tit-for-tat pricing game. What real world data would you want to examine? What would you consider to be evidence of tit-for-tat pricing? How can you distinguish tit-for-tat pricing designed to sustain “collusive” pricing from competitive pricing?

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