What do you mean by "cross exchange rate"?
Are you talking about using arbitrage on different exchanges to profit from? There is really nothing wrong with it, that is how arbitrage works. But somehow you have to also take into consideration the fees of every transaction you have through it and you also need to have funds in both exchange.
how can do that ?can make profit in this way
2 wallet?but how?
For example, you have an account in an exchange platform. First, you are checking the rates BTC to LTC. Then LTC to ETH. And BTC to ETH. I always see some differences between the rates.
That's why you do not need 2 wallets.