A retail operation is one that buys a finished product and adds a markup to resell, but does not add any value to the product or change the product in any real way, such as a grocery store, Walmart, clothing store etc.
a retail operation often uses loss leaders to get people in the store in hopes that they buy other items that are not reduced in price.
The reason we shouldn't do this in a custom manufacturing business such as a sign shop is that our business model is completely different, we buy raw materials (or semi-raw anyways, I don't make my own vinyl) and use those materials to make a finished product. One of the aspects of custom manufacturing is that every job is a bit different, even 2 jobs for posters may have slightly different specs that lead to different pricing.
this is not to say that you shouldn't offer quantity discounts on larger jobs, the economies of scale allow you to do that and still be profitable, however selling 3 posters at a loss makes absolutely no sense.
