You could throw away a few thousand coins at provoking a plunge but if the price goes down and stays down then that's looking like the 'true' price to me. No one can keep a price down for more than a few hours artificially.
there was the bitstamp bearwhale back in 2014. i think that wall took a few days to break.
i agree though. i might give it a day or so to account for banking delays, but if real people are buying/selling a price level for any sustained period of time, that's the real price. that's why i don't buy the BS about willy bots and tether printing either. sure, maybe there were efforts made to pump the price. you think those alone could sustain bubbles (with full-fledged media coverage) for months and months? of course not. real money did that.