- Bad organization
- Bad communication
- No structure nor script ready
- Authors that either talk as if I already knew about their entire story or want me to do more than drawing (coming up with plots, characters, arcs or anything that is not drawing-related)
- Very unrealistic deadlines
I don't usually reject collaborations for as long the pay is good, there is a script ready to adapt or at least the author knows what its doing.
But I would likely reject working for someone regardless of payment if I'm there waiting for them to have something done, be it a script or storyboard, like... I associate that the moment you are looking for an artist, another individual to provide a service is because you already have the material that need to be processed.
I'm used to work with rules and a structure, even when commissions is something that happens. It's either you give me total freedom to mold the work or you give me something to follow strictly, something in between is time consuming and that's how you end up with lots of revisions, corrections, "oh but I would like it better if you did it like this" when I already done the job.
I rather deal with someone strict, that has their vision already solved, that has a stick figure draft but simply tells me "This but in your style" than dealing with someone that is constantly unsure about how to diagram stuff, "what about this angle?", "so what's your opinion? oh... well... I'm not sure now" and just... beating around the bush or having to reject other works because I'm not sure when this person is going to make up their mind and I have to start working and I don't want to juggle my schedule or working hours
Lately, I've only been rejecting gigs but because I don't have the time. I work for two webcomics that are both active on the making (one still hasn't been published), for 3 novel authors's Patreons making exclusive content and then Commissions.....
And then personal projects or interests that have the minimum of quality or dedication but that are done regardless.