If my supplier was selling to joe public for a very similar price to what I was selling them for, I would change the supplier straight away!
Why should I let him have 2 bites off the cherry and affect my profit margins when I buy in bulk and regular and joe public doesn't? The occasional once or twice maybe and that meaning occasionally.
The most courteous way to sort it out would be for say Ima to contact the local trader when an enquiry or order comes through, eg: Stu, Karl, etc, etc and send them the info so they can deal with it and still make some kind of profit on the deal ....it shows loyalty to the trader and the joe public gets it at a good price still ...problem sorted IMO