Contracts Issues in The Blues Brothers

In The Blues Brothers, the band performs at Bob's Country Bunker.  All things considered, the show goes rather well:

 

After the show, the Brothers ask to be paid.  The owner offered to pay $200 for the performance, but the band owed $300 for beer.  Elwood objects that they had been told that they would not have to pay for the first round, but the owner refuses to treat that as a waiver.  A student asked me about the scene, and I'm not sure how it might be resolved.  I would treat it as a matter of interpretation and expect that a court could hear expert testimony about the customary terms of contracts with bands at establishments such as Bob's Country Bunker.

But then there is a second issue (or third, if you think waiver is the second issue).  The Brothers got the gig by pretending to be another band, The Good Ole Boys.  So Bob has an argument that he was fraudulently induced to contract with Jake and Elwood.  If that is so, they might be better off seeking to recover in quantum meruit, since Bob told them "that's some of the best goddam music we've had in the Country Bunker in a long time."  The audience hurled what seemed like hundreds of bottles of beer at the band during the performance, so Bob must have made quite a bit in drink (or projectile) sales.  On the other hand, I don't know what it costs to clean up that mess.

Hat tip to Valpo 1L Brandon Carter for calling my attention to the scene and to the fact that he is watching old movies when he should be studying law!