You wont be able to stop him. Look at his post history, it's all about selling or not being in XMR for entire year etc etc while trolling other competitor coin threads and simply a legend in his own mind.
Just another prick with daddy issues growing up, so he is trying to make up for it by posting about imaginary trades where he probably wants to see himself come out ahead. All coins have these specimen.
Traders will be traders I guess. Monero is hard to get right now without spiking up the price.
Just put in a buy order at the top of the orderbook for a couple BTC, and look at how many 1 btc orders will quickly pop up in front if it. At least 3. You have to fight several people and some bots for every 1 btc buy if you don't want to pay 2-3% extra. Or you put in a lower order and wait for multiple days praying for a dump to happen.