1. Lesson here is that you are negotiating against yourself. Ask yourself this - who buys these items? People who buy them will not care too much if it's 40 or 500. Poor guys like you will just make them for those 12.5g or whatever. Also pretty funny is that buying them for 40g, disenchanting them will likely make profit. Unless someone like you comes and puts "bUt rEaGenTs + pRofiT" price omg. Market decides the price, exactly like you said. I enjoy stocking up on some "righteous" dudes items he sells for "fair price", after some time he is still poor af, drops it because it's just now worth the time. Then I make profit from his items. Why craft and headache these things, if you can just go kill 2 mobs and make same gold?
2. They are buying your work, so they can make profit with 2 clicks, while you run around and craft things. They are your employers, don't tell them what to do.
3. Meh, that guy sent it because he doesn't understand the market, exactly like you. Nothing wrong there, all he wanted was for you both to make biggest profit, he didn't know your are on the crusade.