Yea, they're a useful bunch, especially if you know one. Back when I worked for an e-commerce site, we were deciding if we're gonna implement package splitting CoD (cash on delivery) for multi-package orders, or if we're gonna just slap the entire sum on the first package (this seems like an easy enough job, but when you have many shipping service APIs you have to work with and you have automated CoD back-reporting that goes into your invoicing, it becomes annoying). We did the easier thing and just sent a pre-drafted dunning letter to people who took the CoD-less packages for free and did not pay for the first one with CoD. Worked like a charm.