I spent the last few months trying to build an arbitrage bot and ran into exactly the same issues. If there's a big price differences there's always a reason, either deposits or withdrawals are temporarily offline, or the fee for transferring or depositing is too high, or for some very small coins it can takes ages to transfer (one transfer took 6 hours, another took a whole week!). Otherwise the volume is so low that you basically lose any edge crossing the spread and trying to find enough volume to close out the transaction. I had a small number of trades that made a few pennies, but also a lot more that just sat there and didn't execute at the expected price (based on the bid and ask when my bot found the trade) forcing me to sell for a less optimal price and end up with a loss. I am still sure there's money to be made with this but it takes a lot of work and you would have to search across a lot of coins and a lot of exchanges to find a viable option. Most people, including some very smart people I've talked to, just assume it's pretty easy to do this but if it was everyone would be doing it. Maybe it was 3-4 years ago when crypto was much smaller and less well known, but nowadays most opportunities are exploited as soon as they exist, I suspect a lot of time by the exchanges themselves.