Is it okay to commission extensions to your existing works? (E.g. another story in the (Im)Mobile Gamer / Train Ride Home universe.) Also, if someone isn’t exactly sure how many words they want, can they give you a maximum budget and try to work things out from there?

Yes to both questions!

Updated the ToS to reflect my answer on your second question, btw. Thanks a lot!

Always happy to help. 🙂

By the way, what happens if a commissioner fails to pay during the week after completion and is unresponsive to your messages? Do you have a blacklist? (There seems to be no punishment for someone messing with you beyond not getting a story they potentially never intended to pay for, even though you spent precious time and energy writing it.)

I do have a blacklist, yes. They will get a much lower priority if ever they try and request another commission or I will outright ignore their requests.

As for unresponsive commissioners, been thinking about it as well. As of now, I've decided to notify them at the final days of the week to ask if they could pay or not.

If they won't respond at all, the commission will be deemed cancelled and the commissioner will be notified, half expecting for them to respond. For the story itself I will either use parts of the unpaid story for my other works, or outright post the story at a much later date while removing any sort of involvement they have in the process, which includes replacing their OCs with one-off characters or even my own OCs, editing it a little bit, and other else. That way, I still get something out of the unpaid commission. I'm not sure if this a good idea, however, so any ideas are welcome for now.

Sorry, had to repost this comment, don't mind the hidden reply. As of now, I'll try to sit on this idea for now before posting it in my ToS.