Not all traders has a big knowledge in regarding about trading here in crypto space.
Trading is a platform like in the market where you need to buy some so we can able to earn in it via
selling in the different exchange site platform.
What you're telling is about arbitrage but these days, I don't think that there's still an easy way to do that since most of the exchanges are having close rates for each of the cryptos that they have.
In short, once you have a coin were you buy it in the
exchange it is consider already as your own assets(coins/altcoins).
Yes, you own that asset but remember that if it's on exchange, they don't give you the keys and when you don't own the keys, you don't own it until it's transferred to your own wallet.