Artists, especially furry artists: when you take commissions, please, USE INVOICES. They are a must in the current furry art market. They create a paper trail in which you have full control over what's being said, which means you can prevent misunderstandings (or deliberate fabrications) later on.
They are a way to protect you from chargebacks, and hold your clients accountable - they're also a way for your clients to hold YOU accountable. It's itemized so that your customer knows exactly what they are paying for (this is especially useful if you charge for things like detail fees and extra characters), and it precludes your client putting in anything weird that might get you banned from your payment processor (e.g. "thanks for the furry porn"). On PayPal's invoices, you can enable the option for your customers to add a tip (and many of them will do so).
It gives your client confidence when they commission you because it is infinitely more professional than just saying "please send X dollars to my PayPal." There you're just giving your client a polite "give me my money." With an invoice, your clients are getting a receipt: "These are the specific goods/services for which you are paying."
You can cover your ass by adding seller notes, terms and conditions, and anything else you want a written record of your customer receiving.
Frankly, I not only always send invoices to my commissioners, but I also don't commission artists anymore if they aren't willing to send me an invoice. There really is no excuse for not using them.
