First...if you are ordering direct thru a manufacturer then your price shouldn't be reflecting a middleman....so there's your discount to start.....So basically you purchase barrels from a distributor at the same price as I would(i'm not a gunsmith) since they are ready to ship, where as purchasing direct from a barrel mfg, you would have to order 10? to get a discount to be able to mark it up, wait 6+ months, make sure your barrel order is the correct length, contour, twist rate, caliber, and mat'l, so you,re not stuck with inventory for a year or whatever. I would assume you get a deposit to cover these costs so you are just out your time for placing the order and you get the components you have had repeated quality with.
Second....if you are ordering 10+ barrels you should have 10+ clients lined up to buy them or you are responsible for extended stock....
Third.....deposits..sure....if you haven't worked for the client before......