Don't forget that the true cost of material is not just the invoice from the supplier.
The costs should include the invoice, taxes, shipping, time for ordering and receiving, storage, and other overhead.
When a customer says "why are you charging me $5 for a switch I can get at HD for $.79", they truly don't know what it takes to get this switch to them and don't understand the hidden costs.
Maybe a little explanation on how cost is calculated is in order if you want to keep this customer.
