Sometimes, the person needs the ISK and selling it will allow them to avoid the market. The sale is also immediate. At the same time the buyer received the discounted item. They know that their ISK is going to their friend/acquaintance instead of a random player on the market. In a game where passions run high, sometimes seeing who you brought from on the market can cause an irritated curl of the lip.
I purchased a Vindicator from Kaeda the other day. The Syndicate exploration content has rained Vindicators down upon the corporation. I didn't bring any PvE ships with me. I didn't realize we'd have such a fertile ground to PvE. Kaeda decided to cook and sell the Vindicators with first dips to corpmates. The price was good and I picked one up. Like my Machariel, it will just hang around until one day I might use it. But, I like it. Next I need a Bhaalgorn and I'll be happy when it comes to pirate Battleships.
Kaeda sold the ships to us for, what would be called, bro price. Bro price is often something around cost. It is that time when you sell things to your friends or acquaintances without the market values. It can be from cashing out your own loyalty points, selling a piece of loot from a kill, or transferring a massive savings found in a contract. Bro price can even be transferred from individual to individual. I buy X at bro price and sell it to my corpmate for that same price.
There is one thing about bro price that should be respected in my opinion. That is not taking advantage of the generosity of others for resale. I know that it is not Eve like. It is, however, how I run my personal game. If I am buying something for myself, I will accept bro price every time I can. When I decided that I wanted to fly Cynabals, I went to Ender and harassed him to crack open his stack of cynabal blueprint copies and sell me some. He asked me, "Are these for you or resale?" I was honest. "For me."
Running TCS means I attempt to source my supplies locally whenever I can. I've received mails from people offering to sell me things. I try to keep up with them when I can. I'm terrible at it with all honesty. But, when I do remember, I will directly buy. I always, always make sure its clear that I am buying for sale at my store. The reason is because people are offering me a reduced price due to their relationship with me. If they were not doing so they would sell at market value and take their mark up. I do not wish to abuse that privilege that has been extended to me.
Bro price is not the same as, "my time is free." Bro price is about doing something for someone else because you wish to. If Kaeda had sold me that ship for market price, and I wanted it, I'd have purchased it from him before the Market because of our relationship. However, without bro price I may not have casually picked up the Vindicator.
Learning about opportunity costs and doing things for yourself to save ISK is a different path then extending an opportunity to another. It also brings in the unprofessional thought of what something costs, personally. When discussing ISK and efficiency one is never allowed to insert fun, wants, or ideals into the equation. However, they exist anyway.
My time is not free but it is easily paid for by appreciation for those that benefit from it. Many parts of Eve can be defined in ISK, opportunity, and what can this do for me and mine. Yet, all of those things have to stand upon the bases of interaction and the willingness someone has to interact with you. In this game we cannot force anything and that always has to be remembered. Treating people well, on every level, is a foundation for stability that few things can shake.