Almost every trading business bills the same item at more than one price. Wholesale to the shops, retail at the counter, and a third rate for the two or three customers who have been buying since before your current shop existed. None of that is written down anywhere except in someone's head.
What actually goes wrong
Not the big accounts — those get remembered. It is the medium ones. A customer who buys every few months at a rate agreed years ago gets billed at the counter rate by whoever happened to be free that day, and either you lose the margin or you lose the goodwill fixing it.
It also goes wrong the other way. Somebody gets the wholesale rate who was never supposed to have it, quietly, for a year, because the person billing assumed.
Rate cards in a diary are not a system
A written list works until it has to be in two places at once, or until the person who wrote it is not in the shop. And a price change means finding every copy — which is why most businesses stop updating the list and start guessing.
The idea that fixes it
Attach the rate to the customer, not to the person doing the billing. A price list is a named set of rates — call them Wholesale, Retail, Old Customers, whatever matches how you actually talk about them — and each customer is assigned one. From then on the rate follows the customer onto the bill, whoever raises it.
How it works in BizGST Pro
A price list is a name plus a rate for each item you want to override. Assign that list to a customer, and both the invoice screen and the counter billing screen bill them at those rates automatically. The person billing does not have to know the arrangement exists.
The fallback is the detail worth understanding: anything not on the list uses the item's own default price. So a wholesale list does not need every item in your catalogue — only the ones whose rate actually differs. A list of twelve items is normal and it is enough.
What this does to your margins report
Something worth naming, because it is the real payoff. Once rates live on the customer rather than in someone's memory, the profit on each sale is computed from the rate that was actually agreed — so a margin report stops being an average across three unwritten pricing schemes and starts being a number you can act on.
Setting it up without a project
Do not build all three lists at once. Start with the one that costs you money when it is wrong — usually wholesale — put the ten or fifteen items on it that genuinely differ, and assign it to the customers it applies to. The rest can keep using default prices indefinitely.
The test that it worked: someone else raises a bill for one of those customers and gets the right rate without asking you. That is the entire point.