My buddy who runs a small plumbing outfit had a client ask for a full breakdown of the "shop supplies" fee. He said it was just a line item for rags and pipe dope, but the guy wanted receipts.
Ever notice how this happens everywhere now? People want to see the breakdown for everything, from a restaurant bill to a medical charge. It feels like a general lack of trust in how prices are set. Adding those notes is a smart move, it probably saves you more time in the long run by stopping the questions before they start. I get a few billing questions, but mostly after I switched to simpler descriptions.