additional "freight" charge added to the bill for goods or services by an unscrupulous businessman or retail worker. For a "normal" or regular customer this charge would not be applied. However the person charged for dummy freight would appear to be of much lower than average IQ. Similar to asshole tax.
Boy the boss is going to happy with me! I just hit the last two customers for dummy freight. I'm going to get a raise!
worker :"That will be 100 dollars sir and then you have your dummy freight which brings your bill to $120."
customer: "Duh. OK."