Is there a way to make money trading BTC if the platform you use is delayed to the actual price?

Let's say a person has $5k in cash they want to invest in crypto (we will just use BTC though for this example).
They open an account and see on the trading platform BTC is worth $4,000. But there is a website that is more up to the second that shows BTC is now at $4,100. You buy the BTC for $4,000 instantly and within a minute it is at $4,100. You sell the BTC because you see on the website is it now down to $4,050.

Someone I know claims they have been doing this for years and they even trade short BTC stuff like BITI using the strategy.

Total BS or an actual hack? I was thinking there is no way this is a thing because then everyone would do it. I also think most platforms (i.e. Robinhood, Coinbase, Binance) have even changed my trading amount a little to reflect the actual cost of the crypto, which is not always what is on the screen so therefor this hack would not work...

Now I can't stop thinking about it lol...