I don't mind correcting the odd spelling error and grammar for the stories I'm an editor/owner but there have been more than a few chapters up for review that I had to refuse because the person didn't bother even trying. Seriously, everything these days has a built-in spell check, even the site's text editor! I had one person who I declined the submission multiple times even after I told them the reason (horrible spelling errors, no grammar, one giant paragraph, etc.). Another thing that ticks me off are people who submit one chapter and never follow-up, leaving that thread dangling.
Some people just can't be bothered. No idea what to do about that. However, perhaps making a requirement of new contributors that any material they submit should be at least two or three chapters long? You could insert a sort of contract in the story description: "If you wish to contribute, please show me at least two drafts first," for instance. I reckon that might conceivably discourage low-effort works, if you're not worried about potentially scaring a few ok people away.
That could have many reasons, maybe they just wanted to give a prompt or simply felt the chapter wasn't well recived. If you're very dedicated and organized, I can understand how that could be annoying for you.
So, most CHYOA stories, then. Seriously, nobody here is trying to pass a high school English course - most stories would get a big fat F, anyway - and unfortunately, many authors have the notion that, since nobody is explicitly asking for basic quality anymore, they need not supply it. I do not mean to sound pretentious when I say that the standard of writing (in terms of grammer/spelling/etc.) on CHYOA is questionable at best. After all, readers evidently don't mind, and it makes the site more welcoming for newcomers when not every story is a masterpiece. Improving oneself is better than thinking oneself a master already. That said, it's your story, and you have the absolute right to reject submissions that do not meet your standards. There is a certain attitude among a minority of users that all stories should be open and free for anyone to contribute to, like Editthis*; do not let them pressure you. Nobody else has the default right to your work. If you want contributions to meet certain criteria, that is absolutely your decision. This is true even if authors have a good reason for their subpar writing. Publishers aren't under any obligation to pay special mind to anyone, and neither are you. * Yes, Editthis technically has public/private/do not edit, but there's nothing physically stopping a user from adding to a story, especially when it's been abandoned or finished.
On the other hand, silver lining... it's nice that so many people are enthusiastic about adding to your story! My brother and I act as editor's for each other's chapters, so I'm lucky in that respect. Still not perfect... but it does help to have a second set of eyes! Just a question, but do you have the ability to edit chapters submitted for review? If so, maybe if there is something worth salvaging there, you could touch it up? I don't know if that's considered bad ettiquite and it certainly shouldn't be on you to have to do it, but it's just a thought.
It is technically possible to edit chapters in review. I guess the best way would be to ask the author if they are fine with changes or to show certain things and how they can change it. (kind of being a mentor)
I am one of those non-native English speakers and my English writing skills are very questionable. Sometimes I do my best, sometimes I don't (It is not a paid job. It is my entertainment. 1) There are tons of tools like Grammarly. If you are a non-native speaker - use them. 2) If you are asked for good Grammar in guidelines and you are not sure that you can provide it - don't add to the story. 3) Don't expect that owner of the story will have fun proofreading and editing your contributions. If they choose to do so - be grateful. 4) Big, well-developed stories ARE NOT the best place for you to start writing.
I have done that in the past but unless it's the odd typo I just outright reject it. The person who set off my initial rant kept submitting the same chapters with little to no changes after I told them to fix the typos, grammar, and use paragraphs (I kept getting a wall of text). I'm not a great writing (professionally I'm a visual artist) but there are tons of resources online out there so there's no excuse these days, especially with built-in spellcheckers!
That's fine. If the user submits the material without any editing attempt again and again, I'd recommend reaching out to a moderator.