Yes, I too have noticed a number of very questionable posts attached to questionable accounts. I confirmed that one was certainly plagiarism but another, that I was sure to be, came up clean in the checker. I hadn't considered the probability that crafty rewording may have been at play.

Rewording or not, plagiarism can be spotted without the checkers (but they help for confirmation). People have a style to their creations and when that style is inconsistent, red-flags go off.