How to deal with vendor that brings wrong items?

i used to deal with shady beer vendors who would not rotate the beer and try to short you a few cases here and there. plain and simple, don't put up with it. i was young and they thought they could scam me. i would stand there and watch them and count right with them. many vendors are known for this! you and him have a contract, it may be in writng or be verbal. he still has an obligation to hold up his end. tell him you will not pay for services not recieved.