Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
i see this a little differently. contract customer is another business and he is reselling them to the end user. I would have printed the job as the responsibility for copyright checking will lay on him and not the printer. if there is an issue the lawyers will not know you printed the shirts they wil come after the dealership and him as they are the ones using the logo not you.
Just heard on the radio this morning about an artist up here , that saw her designs on shirts in Marshals , She contacted the major retailers that had her design on shirts and was basically told to stuff it and here is the last known address and contact for there LA manufacturer/ screen printer which were all dead ends, It will be interesting to see where this ends up a news Fraud show has picked it up and is asking the questions now.