When do you imagine that the price changes? After Richee McGee has sold all he wants at the high price or as he is selling?
The price always moves against you. More if you do large, less if you do small. There is no profit here, only paying more or getting less as you go. When you try to go the other way afterwards, same thing happens.
I'm not convinced that it is entirely safe. Imagine for a moment huge investor A and huge investor B. Neither of them will be fooled by the other large investor, but they can cooperate. Let's say that investor B is a bank with millions of suckers, eh...excuse me, millions of customers who they manage investments for. Investor A sells an enormous amount of gold to investor B who knows that the price will drop after the transaction since the gold will become spread out and dilute the small investors' gold. Why? Because investor B buys the gold at the high price for the millions of its customers! Then after the transaction, both investor A and B wait a while (hours, days or whatever it takes) for the effect to be reflected in the gold price, and when the price is low enough they both buy gold. Both investor A and B become winners, and the millions of customers losers.
I don't trust current markets for a millisecond.