Cancel? Then the user is actually doing it. But some exchanges make trades using bots and execute them purposely to increase the volume of the coin so the cancelled trade may not add up into the volume which means exchange has no reason to do it. But how can you find the trade is cancelled not just executed?
Pretty simple — the exchange order is not filled/executed if the price didn't reach(or not even reach close to) the price of the buy/sell order. Like, I can place a buy order right now on BTC at $20,000 and expect it to not execute any time soon(or possibly ever, unless we get an exchange crash due to lack of liquidity).