I would say the biggest problem is liquidity because I have seen that there are coins that trade for higher on some exchange while lower on others but you have to keep in mind that the buy/sell orders are enough for you to buy and then quickly sell.

I mean, I remember an instance where I purchased a coin and until the time I withdrew and deposited to the higher price exchange the trades vanished and I ended up buying a coin I don't know about and I had to immediately sell it for a cheaper price and so eventually it resulted in loss so make sure when you do arbitrage trading you make sure the trade volumes are big enough and stable enough otherwise you might struggle with trades.