'in and out' credit?

[yusunghee]

hey guys,

i sound stupid for asking this question, but what does the term 'in and out' credit mean?

i work as one of the buyers for a supermarket chain. i bought some merchandise, but it was billed wrong.
i called the sales rep up and instead of sending me a check/credit, he says he will do a 'in and out' credit.

can someone please explain what that means?

thanks!