> For items where the cost per unit is dependent on marginal cost of each item, it's 'fair' or 'efficient' if it is priced with a reasonable markup over the mar

> For items where the cost per unit is dependent on marginal cost of each item, it's 'fair' or 'efficient' if it is priced with a reasonable markup over the marginal cost. With the quote marks, I'm not sure if you're being serious or not, but a fair deal is one that both sides agree is good for them. Now often, there's a range of prices that make sense for the seller to sell at (anything $40 or higher will be fine for them) and a different range that is okay for the buyer (anything $60 or lower). Anywhere between $40 and $60 they can do the deal and be happy, and it'll be a fair deal so long as it's voluntary and nothing crazy is happening. As for efficiency - again, there's no ideal profit margin. If anything, if you really like a field, you want higher profit margins in that field, because it encourages new competition and investment and innovation. Getting good value is more important than ensuring the person selling is making a small margin. For instance, McDonalds only marks its food up a tiny bit, but it's still not a good value for me because I don't value McDonalds highly. But there might be some Brazilian food that's marked up 50% or 80% that seems like a real bargain for me. tl;dr - "Everything is worth what its purchaser will pay for it." Publilius Syrus, ~100 BC in Rome.