Certainly all red flags are different, but here are just a few of mine.
“When I originally wrote this it was 325,000 words. Realizing that was much too long I split it into a trilogy...”
You know, a well-written book cannot simply be divided. That means that somewhere in the middle of your book the story ended and another, completely different story took hold. Either that or you simply cut the book in thirds, and I’m going to have to read three books to be able to actually finish one. The author often makes this sound so simple, like you just split a book. Even if that’s what you did, ultimately you would have had to rewrite all three books to make it work. At least that’s what I think when I hear that. So even if you did split a book to make it into a trilogy and you feel it was successful, no need to tell me.
"I love reading [name your genre] novels, but never find anything that I think is really good, which is why I decided to write this book..."
I think it's pretty obvious here that the author probably doesn't have enough of an understanding of the market or the genre to be able to write the book. Now of course I could be wrong, but do I really want to represent an author who doesn't respect the genre she's writing in?
"My book still needs editing..."
Almost every book I offer representation on needs some editing. A tweak here or there at the least. If you think your book needs editing, at a time when you should think it's ready to be published, imagine what I'll think?
"I've attached chapter [any chapter other than chapter 1] since this is when I really feel the book gets started."
Why wouldn't your book start at the beginning?
"I wrote this book in three weeks."
I know people do it. I know they can, but I have to question how a book could have been written, edited, and revised in three weeks. And I'm talking a full-length 80,000-word novel here.