I read somewhere that companies that do a lot of ACH payments use different accounts for receiving and sending payments. The receiving account is locked so that it can't send and the sending account is supposed to stay secret. I don't know if that actually works in practice, though.
Yeah but for 90%+ of transactions, if you are being paid by a company, you can almost always request a paper check instead of an ACH transfer (sometimes with a fee). In that case they either have yet another account for check writing (which won't be "secret") or they give away their "secret" ACH account.
