The last sentence is what I consider the main key of doing business.

Both sides must consider the deal they made a good deal.

This of course means for anybody considering a deal, that you should not do it if it is clear that the customer can't be content with what you deliver because of bad specs, general uselessness of the product or plain overengineering of a process that already works well without computers.

Creating a win-win situation should always be the goal in negotiations; if your partner feels like he's got the bad end of the deal, he'll have to try to press you harder later in the project to get out the moneys worth without paying more.