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Here is How:
Every exchange has a different price point for each Coin based on volume, market and liquidity. On some exchanges prices will be way cheaper then on others.
For example Binance:
https://www.binance.com/?ref=11289220
Ripple is cheaper there so I will usually buy it there.
Then transfer over to Poloniex and sell for the current usually higher markup.
Best example was Litecoin when during its second jump I bought it at $290 when it was already $315 on Gdax. Transfered to Gdax and sold for $390.
Easy Money......