How are commissions usually submitted?
They are submitted by any means of communication that you, as the vendor, designate as acceptable. This means "Email me," "Call me," "Note me on Deviant Art," or all of the above. For commissions with others online, email is usually the best.
Should I set up a separate account only for commissions?
If you designate email as your primary method of contact and your email address looks amateurish, you should for the sake of appearances. People will move on to a new artist for the smallest of reasons, so you want to get rid of everything in between you and opportunity, including the possibility that they may think you are immature because you have an immature email address (if you have one).
How do you know if you should set up a new email address for sure? Well, for one, would you NOT want your boss or your mother to know what the email address is (pragmatically speaking), like "bigtitties24@email?" Does your email make reference to a fandom, like "findingmysasuke@email?" Is it incredily long or hard to remember?
At what point in the process should you ask for payment?
As soon as the commission that your client has in mind is clear enough that you could, in theory, actually create this thing they're wanting (or a phase of it, for complicated projects). You ask for payment
before you do any work at all whatsoever, or some portion of it as an insurance against those who run away with your work without paying.
There is such thing as "spec work" which is "Make me stuff, and I'll decide what I like and whether I'll pay you," and there are people who do agree to doing work before getting paid for it. Do that at your
own risk. Just because someone is nice to you doesn't mean they'll actually pay you!
What if you can't complete the commission?
1. Cover your bases before you start by asking whether this commission is time-sensitive and having a refund policy somewhere (a terms of service, like on a Google Doc which is publicly viewable).
2. Approach your client and say that you aren't able to complete the commission, whether at all or until a certain date. If it's until a certain date, and you want the opportunity to finish it, discuss with your client what THEY are comfortable as a course of future action. Usually you will want to say "I can't resume work on this until <Date.> I'm very sorry for the inconvenience. Are you comfortable with waiting until <date> to reconvene?" If they are, good! If they're not, enact your refund policy.
Refund Policy: Every artist has their own idea of what is and isn't fair for a refund policy. Find out what is good for you personally, and find this out BEFORE you start commissioning people. You can change it later, so long as you don't change it on a client you currently are working with.
do i have to send the commissioner a print of their art or is the digital copy enough?
Usually, people are satisfied with a digital copy. It is of relatively little trouble to send them two files: one for display online (72 DPI) and one which is high quality for printing (300 DPI). Remember that it costs money to send prints!
What happens if a commissioner reproduces their commission and sells it? Are they allowed to do that?
ETA: Lol I misread that question as "Can I resell what I sold to a client as a print." State your terms first before going in, whether by a general Terms Of Service that says Don't Do That or a contract specifically written between yourself and that person. Approach that individual and tell them to stop. They usually won't because they didn't care in the first place. If they're selling it on some place that is like Cafepress, contact the source next and ask them to get this fixed. Try to signal boost your plea with social media, but be respectful doing so.
can i legally accept commissions for fanart?
Again I can not give you legal advice. From what I understand as a non-lawyer, though, the answer is, "yes, you can." Here is an in-depth response to that question in
The Truth About Selling Fan Art.
If you live in the United States, save 20% of what you make off of commissions in case you get hit by the tax man.