On the plus side, there's also often very little motivation for the person doing step 2 "provide a PO number" to not sign up for a dollar amount that comfortably covers your expected "interminable amount" of time you'll be providing their purchasing department with credit. You _do_ need to anticipate and factor it in up front though - you can't come back 4 months into the process and say "hey, the price just retroactively went up because you're so slow paying!".
