Bro... Calm down, read through the inputs from other members and digest it. I've never experienced this and if a dispute arises, it could be used against you. If the price of bitcoin depreciates after displaying your selling ad on Binance, you can delete it and create another one which should be a round the current market price. A vendor that's okay with it will buy at the price you set, you don't need to negotiate in the chatbox.
You are right, I don't even think that we could negotiate a price while the ad with some specific price has already been set by either the seller or buyer. I would hate p2p if there would be any negotiation, and why do we even need to negotiate, when we have hundreds of other exchanges that we can use for p2p trades? This is just so unreal for me.
But still, as many members have already said, scammers try everything, and I also think the ones who try to negotiate with you on Binance must be scammer, I already have read many cases opened on BTT that how scammers find new ways to steal money from you on Binance specifically. Now this method has got my attraction. The last was a loop in the policy, now this.