> The title would be better written as:
> "San Francisco Apartment Rents Crater, up to 31%"
No, it wouldn't. The comma makes the “up to” phrase bizarre and detached, and does nothing to improve things. It would only make sense if it was trying to say the rents both “cratered” and somehow went up (though what the % would be measured against in that case is hard to understand.)
As a sentence, it would read better with a “by” after crater, though it would be even better (and be a more accurate title) if it dropped the “up to” and just gave a single measure of the drop rather than one end of a range. “Up to” is a clickbait term that always obscured rather than clarifies.
I'm always amused by "up to" in advertisements and such. "You mean you promise me there won't be any discount over 40%? Good, I was really worried you might give me 50% off in some cases."
"San Francisco Apartment Rents Crater, up to 31%"
meaning, the rents fell drastically, by as much as 31%.