The simple answer is that you should get paid when someone is profiting from your labor.
…However, providing content or services to a friend without being compensated does not mean that one is being exploited. If the terms of the exchange are mutually agreed upon, and if one person isn’t immediately monetarily profiting from the labor of the other, then it may well be a fair exchange, and one that is part of how solidarity and community are built within the field. W.A.G.E. advocates for equitable compensation, not for the total monetization and commodification of every aspect of our lives; we leave that to neoliberalism.
—W.A.G.E. as quoted by Bean Gilsdorf, Help Desk: Support for Artists, Daily Serving, May 25, 2015