When I was buying / selling property, the only way I did it was win-win, and it is quite easy. The simplest solution is to listen to what somebody needs. If someone doesn't win (win-lose, lose-lose), you get a bad reputation and some people retaliate (personally, or bad-mouth, or physically).
For example, I once bought a duplex on a contract that had no price attached to it. The widow inherited it, was losing it and was going to lose her main house as well. She wanted enough money to pay off the duplex, pay off her main house, have 10K spending money, and enough money to pay a contractor to remodel her main home. Well, contractors are expensive and I had a crew that could do the same thing, so we negotiated all the terms, except that I would do the remodel instead of giving her money to pay someone else. She got all the repairs she wanted (I even didn't complain too much when she wanted a $1200 bathroom vanity instead of a more reasonably priced one) and I was able to save over $20K in what she would have wanted to pay someone else to remodel the home.
Even houses that I have sold "as is", if something went wrong within a month (or a few months) after someone moved in, and it was something I could not have known (but would have fixed had I known), I have sent my crew over to fix it, even though it was "as is".
Doing computer programming, many people take shortcuts. I tend to give the client more than what they expect, to get repeat business. So, I may be doing extra work up front, but I don't feel that I "lose" as my extra time, to me, is an investment in goodwill and future business. Even if it is a one-time deal, a reference is always helpful.
On several occasions, I made a verbal agreement with someone only to find out that I could have gotten a better deal. I stuck to my word, and in 2 instances that I can remember, it paid off. One, I had sold a car to someone that I could have gotten more money from a dealer. I ended up later working for this person by not backing out and making $400 more. Another person ended up being a good source for financing my properties (and I ended up working with this person on several houses as well).
