Has anyone ever seen this before? I posted something for sale on Craigslist, and someone responded with interest but (1) said they "don't reply from cl mail" and telling me to email a different address and (2) more weirdly, below all that is pages and pages and pages of what looks like a children's book text. The text is actually in white and I only saw it because I was in dark mode. I looked later in light mode and you don't see it at all.

I should be clear: I get that the book text is almost certainly designed to get around spam filters. I see that all the time in... spam. But why is it in a CL reply?

And is it enough of a red flag to avoid?

@mmasnick I'd look at it another way .. Is there a legit reason to actually have that in an email? I wonder if it's a spammer who had it all set up for something else and because it's hidden, they forgot it was there when they sent the email..
@XenoPhage @mmasnick that's my guess - back when I did pen testing we'd test client training with phishing messages and I pasted Dickens into a comment block in our email template to add length and get around length heuristics in spam filters.
@mmasnick If you have to ask, I'd say the default answer is "yes".
@mmasnick Might not have a specific purpose in this context, probably just built into whatever spambot software they're using.
@mmasnick Sometimes seen something like this on web pages, hidden in comment.
@mmasnick It’s in the CL reply because they are likely scammers who bulk reply to a lot of CL posts and are trying to avoid CL filtering them out. In this case, it’s not your spam filter they are trying to avoid, it’s CL’s.
@mmasnick red flag, report it to Craigslist
@mmasnick Yes. That's a scammer forgetting to clear the text. Report them.
@mmasnick yeah. It's either leading to an account takeover attempt of your email or obtaining your bank account info for a "wire transfer."
@mmasnick Ignoring the weird text in the email, the "'don't reply from cl mail' and telling [you] to email a different address" is a huge red flag by itself and you should definitely ignore this person and optionally report them to CL.