The typical "dealer" holds a job and sells to pay for their own use
"Earnings for drug selling were positively correlated (though weakly) with legitimate earnings. Drug selling seemed to be a complement to, rather than a substitute for, legitimate employment."
Reuter, P., MacCoun, R., & Murphy, P., Money from Crime: A Study of the Economics of Drug Dealing in Washington DC (Santa Monica, CA: The RAND Corporation, 1990), pp. 49-50.