1-Do i know/trust the people?, if not, then i ride the nope train.
2-It is entertaining?, if not, then i ride the nope train.
3-A charity from an organization i trust?, if not, then, nope train.
4-Do i have enough time to embark in this?....if not......nope train
I also like to flirt with the idea too 
When I first joined the forums, I was actually really interested in a collab 
Especially unpaid, because I pretty much just started drawing. However, it was also really intimidating to approach people (I didn't start posting yet), so I found myself stalking profiles a lot looking for:
But I think that the most important condition would be "time" right now. 
for me
Nothing. I can't subsist off good will alone.
In a more detailed answer: I'll work for no pay if the project honestly sounds amazingly interesting and like something I'd be involved in as a hobby. But if it's something that is even remotely like work, then I'm out. Anything with tight deadlines, turn arounds etc. then I'm gone.
Like someone mentioned above probably only if it's a zine I'm interested in or some kind of community collab (like ya'll did for christmas) but other than that the chances of selling me on an unpaid collab, especially when I've got projects of my own I'm looking to pursue, are slim to none.
I might be swayed into something very short like a couple pages but it'd have to hit some of the same points @Rhonder brought up, like pitch presentation, familiar faces, and for me personally shared workload. For a straight up unpaid collab I think the only way a person can make it at least a little worth it is some kind of exchange of services otherwise it's kinda....eh.
If I’m bored. I wouldn’t do a full blown comic or novel but I would happily do art for a novel, a cover, and thumbnail.
1) I have time. Which is rare.
2) I know the person, and they are trustworthy and honest. That's more important than their style or prefered story genre.
3) Both the person and I are aware and fine with the fact the deadline may be changed, but both honestly try to avoid multiple delays.
4) The project is at least somewhat off the beaten track.
5) IP concerns and potential future uses are discussed beforehand.
6) Project is short or in small modules somewhat independent.
The likelyhood of me jumping onto a thread for unpaid collaboration in this forum is... EXTREMELY low, lol. Even if I'm starting to get to know some of you guys (which is great! Yall are cool peeps) I dunno if I'd be willing to start anything with a stranger or near-stranger without feeling secure in that the project would definitely pay off in some way..
That said, I guess I am doing free work, just in circles of very close frends and on stuff that I'm excited about! I'm in a fanzine, as has been mentioned above, and me and a couple of friends from uni are playing around with a game project idea. So those kind of things are the execption 
Something small, I have the time, and it's someone who respects the problem with it being unpaid. Which, usually, means it's a charity zine or someone who really wants to support someone else and pays in other ways, or a friend.
1) If it sounds fun (if I'm not getting money, I'd better at least have some fun)
2) If the collaborator(s) has a talent that I otherwise would never have access to (like GAME DEVELOPMENT)
3) If it'll be a chill, casual experience (I'm okay with having deadlines, but not with chasing them every week)
4) If it's a short term project (that's always nice)
...That's pretty much it. ^^; I'm a relatively easy sell for this kind of thing; the biggest issue is that most unpaid collabs I see don't sound like fun to me.
If it's a charity I really believe in, otherwise if there's someone I admire that I want to do fanart for--I'll just do fanart.
...like to be honest I'm over 30 so I feel like if you can't pay for your collab, you might be so young that it'll be stranger-danger for me to work with you. Older people have expendable cash (usaully. Like right now it's Covid, but in a normal world, people will pay for services)
I'm an artist so what I'm lack off is writing skill. So when I see a "writer looking for artist" thread, I would like to see their their previous/example works. And if they already have a story for the collaboration, beside the summary and genre, I would like to see the ready-to-go script of one or two first episodes. It it's click with my liking, I'll send them my art example, what I good/not good at and what I can't draw as well.
I will skip the I have this idea or dm for more detail threads.
I've made a couple of free art like covers and character design to practice something out of my comfort zone in order ro upgrade my skills. By that I mean drawing something which isn't auto approved by me by default because it's just my art but something that another person would like and accept beecause they like it, not because they paid for it. My art isn't great that's why i do it fo free and I also don't like when ppl charge 20$ for a picture worth to be hanging on their fridge exclusively.
I probably wouldn't accept an unpaid collaboration here on Tapas because a reader probably wouldn't care who drew the pictures if it's not mindblowing. Other platforms, such as Youtube and Instagram (I don't have an Instagram though), I would if they have a large audience, and if I feel like I can help them. I wouldn't collaborate with a stranger on the internet, but if I'm real friends with them in real life I'll collaborate for free.
I will only do it if we've been friends in real life for a long time and some of the characters have to be mine. My friend and I actually do have a collab series of our own.
Well, I do lack greatly on the writing side so I do search for comic collabs. So, first and foremost:
• A good writer
Be able to create a story from start to end, with good dialogue, be clear and think on details (don't be lazy! describe or use references for characters, locations...)
• A story I love (and that can be monetized)
My final goal is always to profit from the comic. I'm not working for free, this is an investment lol so I have to think this story is so awesome that we gonna get rich or smth. But till then I should at least feel entertained enough.
• A good relationship/profesionalism/respect
If I sense a disturbance in the field I will start being less and less motivated till I quit. No winning award story can make me stay if the other person is a lower back orifice.
• Fair workload, equal levels of commitment and fair pay
If the other person writes a chapter and disappears for the month it'll take me to draw it, if they're not willing to try and reduce my workload one bit, and on top of that they expect 50/50(if profits are involved) well, you can imagine...
I have a few very narrow circumstances under which I worked unpaid with a writer:
Both of the above comics were black and white with little to no toning.
So overall my rules are:
