When you read carefully, you see how this applies. From Charity and Its Fruits:
And they, also, are of a spirit and practice the very opposite of a spirit of love, who show an exorbitantly grasping and avaricious spirit, and who take every opportunity to get all they possibly can from their neighbors in their dealings with them, asking them more for for what they do for or sell to them than it is truly worth, and extorting to the utmost from them by unreasonable demands: having no regard to the value of the thing to their neighbor, but, as it were, forcing out of him all they can get for it.
And they who do these things are generally very selfish also in buying from their neighbors, grinding and pinching them down to the lowest prices, and being very backward to give what the thing purchased is really worth. Such a spirit and practice are the very opposite of a Christian spirit, and are severely reproved by the great law of love, viz., that we do to others as we would have them do to us.
In other words, “think win win” is not a modern invention. As Edwards points out, even in our commercial and business dealings, Christians are to have a view to the good of the other person. We are not to simply seek our own benefit, but are to have regard to what will be good for the other as well.
This is not anti-capitalistic, either. One of the best recent books on negotiation, Getting to Yes, makes the case that this is actually the most effective form of negotiation. It’s called thinking win-win, and it’s not only the most effective long-term (since people don’t like doing business with those that are always pinching them down to the lowest possible amount), nor only the most decent way of treating others; it’s also very Christian.
Christians seek the good of others–not just in their personal lives (what does that even mean, anyway?), but in all realms of life, at all times.