Sentence:  These booze <WSD>customers</WSD> had until then been buying their supplies from the Sheldon , Saltis-McErlane , and Druggan-Lake gangs , and now they were competing for trade with the Torrio-Capone saloons ; once again O ' Banion 's brash recklessness had caused a proliferation of ill will . 
Meaning of the word marked with <WSD> tags:  someone who pays for goods or services