Respect yourself. Respect your work.

If someone is asking you to do work for them for free, stop and think about what that means. Nobody gets up to go to work on any given day hoping that their employer will like their work enough to decide to pay them at the end of that particular day. People show up to work because they know that, even though they may get fired if the work they do isn't up to par, they're getting paid until the end of that particular day. It's not like buying a lottery ticket.

If you buy a drawing from an artist, they may show you a sketch of their progress to give you a chance to make adjustments, but once they've drawn the finished piece, especially if you had access to tons of their artwork where you could see it to get an idea of what you're getting, even if you decide that you don't like it, you may decide not to commission that artist again, but you certainly owe them money for the work they turned in at that point! This is true regardless of whether the situation applies to a visual artist, a writer, a musician, a translator, a suit maker, any artist as the case may be.

Corporations love to hire interns for unpaid internships. This is always a terrible decision for interns! The same thing often happen when people with an oversized sense of entitlement end up "crowdsourcing" much of the work that goes to their bottom line. This is especially true for idea work! Remember when Kramer shows up at Calvin Klein suggesting "The Beach", gets laughed out of their office, and moments later they come out with exactly that? People who want your ideas for free can do whatever they want with them after they pretend to reject them. It's called taking advantage of people.

You'd never get on a bus, and expect to only have to pay bus fare when you get off the bus if you liked the driver's driving. You wouldn't go to a restaurant, order three meals, try them all, and only pay for the one you liked best. Money and work simply don't work this way. When someone puts in their time and effort, regardless of what form it takes, especially if they bring considerable training and experience to that effort, given that it's time and effort that they can't dedicate to other ventures which could be profitable for them instead, it deserves compensation.

If you're an artist, don't be Kramer, and *gods*, if you're a commissioner, don't be Calvin Klein.
Respect yourself. Respect your work.