Drug dealers are naturally leery of new customers for fear of them being undercover agents. One proven way to ease the fears of the trafficker, as well as defeat the entrapment defence, is to make a series of confidence buys.
A confidence buy usually starts with relatively smaller amounts of drugs and progresses to larger quantities. The objective is to make the suspect feel comfortable selling drugs to the undercover agent later since he was not arrested after the initial transaction.
Global Drug Enforcement: Practical Investigative Techniques, Gregory D. Lee