Where a worker was told to collect his salary from a merchant, and now both merchant and worker come to the Employer demanding payment/reimbursal: Bava Metzia 3a, 6a
Where both a merchant and a consumer claim an item is entirely theirs: Bava Metzia 2a, 8a
If, between a merchant and a consumer, one says it is entirely his and one claims half: Bava Metzia 8a