A while back I did an Iron Artist challenge to fund a new computer. Of the 100 orders I filled, one person requested I draw two canon characters together instead of the more typical canon character + customized player character. So I drew the image and sent it off, got the client's approval and continued on with my work.
Now, around three months later, a third party's come to me and asked for permission to use this image in their tumblr theme, and I wasn't quite sure what the proper protocol was. Eventually I responded and told them that it was fine with me, provided my signature stayed intact and credit was given, but that they should ask for the commissioner's permission, too (since they're the person who paid for the image's creation in the first place).
Was that the proper thing to do? I know the lines around drawing fanart for pay are a bit muddled, so I thought I'd ask around for a second opinion.
After reading the responses here it's clear to me that I didn't do things exactly right this time around - I should have made the commissioner's consent non-negotiable. If this does happen again in the future - and considering the amount of fan art I'm asked to draw on commission, I'm certain it will - I'll be asking the commissioner directly what they think before responding to the third party at all.
Thanks for your thoughts, A_B!