I'd say the deciding factor is how they respond to your requests. No communication? No sign of progress and constant excuses? Might be time to put out a warning.

Personally, I've given up on ever getting my piece from Jailbird. :(

I only ever had one commission with her, wanted to get more - but she kind of melted down after that. She needs to realize she is headed down a dangerous path with burning customers while taking news ones.

She's not the person I am waiting on, however.

Up to you. But artists are real flakes. Some of them have jobs and lives and all sorts of distractions like youtube.

It might be he expects YOU to email HIM and be a "nuisance."

If he's overdue, he really should EXPECT you to get on his case about it.

If it's all informal and whatnot, that is.

If he has legit terms of service you can look through regarding communication and commission status, that would be a good place to go and work out what to do.

The fine line I do not want to cross is being a pest. I've read way WAY too many tales of people pestering like every day - which I will just not do. Sadly, this person does not have a formal Terms of Service that I've noticed.

Well... My definition of "not being a pest but honestly making sure lines of communication are still open" is an email a month. Unless you're asking for a custom deluxe color 36 page comic, I'd think there'd be some progress in a month.

Up to you. Sorry if being all "I need to solve the problem" rather than "I should be there to listen to your problem."