Well, some free stories reach 70-100KB in text form. More like a novella size. Some readers "complain" they r too long! LOL Yes, my free stories are basically XXX. Yes, maybe I can split them. Is there any word count limit for each post?
Regarding commercial stories, is short summary (or XXX scene excerpt) considered advertisement? I'll just write what it is about. Then the end. No purchase link, no "buy now" sentence. Just sharing the story summary, perhaps like movie articles we read in movie magazines. We don't consider movie articles as movie ads, right? So something like that.
If I'm allowed to be honest, I think... even IF blatant ad were allowed, I really doubt it could bring any sale. I joined an ebook forum (similar to this forum - err... you know, sharing forum) and the mods allowed me to put blatant ad banner and link, the result: zero sale