It was a lot of logistics with physical cash. But yeah I tried to run it as close to "real" as possible in case I did hit legal issues (isolating the entities, not comingling funds). Also, had to make sure for taxes that the cycled cash wasn't possibly viewed as income to either entity. There were a few optimization steps I found that helped me streamline the logistics but I still was withdrawal-ing cash from the ATM business account daily. To start the cycle over again.

I kept a small amount in the consumer accounts. Maybe $300-500. The cash took 2-3 days to do the loop if I recall. And this allowed me to keep do multiple $20 withdrawals each day on each account.

It got big enough that I employed someone to sit at the ATM and make transactions. Then I bought 2 more ATMs so they could multitask / reduce idle time during the 1 minute it took for the machine to process and dispense.

I stopped it when I realized the numbers were getting kind of big and a few banks had caught on and closed my accounts. Then because of the physical cash, I was worried about getting robbed. I was getting very paranoid about the whole thing and decided to wrap it up. I remember meeting a few times with attorneys during it to get varying opinions. Over time, the advise turned into "we think it's legal, but you should really stop it".

There was also another smaller but pretty invisible loophole I found with interchange. I could set the surcharge to $0 and so long as the cardholder bank didn't charge "foreign ATM fees" then I'd make about $0.50 per transaction. Much smaller, but order of magnitude more banks offer this feature versus the surcharge rebate feature. The surcharge and the rebates were line items on the bank statements. So, any person at the bank that looked at my account could see the fees and that it was costing them money. With this hack, there was no line item on my bank accounts (only the amount withdrawn). So it looked like the ATM owner did not benefit at all. But, in the background the ATM owning entity received ~$0.5 per transaction of interchange fee.

It sounds stupid, but at the time, my idea was to test this out and then sell a 'get rich quick' style ebook explaining how it works.