[makeitdouble]

Don’t payment gateway request an initialization procedure that registers the POS with the remote gateway ?

During that procedure the terminal unique ID is sent, and depending on your environment, if you have a stable outgoing IP the connection might be filtered on that as well (assuming you do that on site, not at a POS provider). Jumping through a bunch of hoops you might still be able to hook a POS on another merchant account, but once the issue is detected there would be enough info to reverse the transactions (doing that after capture could cost fees, but it’s still better than nothing).

Looking at the delays between the transactions being cleared and the money appearing in your bank account, even with the best timing you might not see a penny of all of that.