How can someone use the account number to withdraw money without my consent?

They can use your account number to game your banks phone support and try to phish their way into your account.

Banks have gotten very good at combating this, but theoretically with just the address he lives in, your name, and a bad bank phone rep, he could get into your business.

The account number would just be one more piece of information to lead with.

I have 1 savings and 3 checking accounts with the same bank. Would they be able to gain access to the other accounts?

Dependent on how imcompetent the bad bank rep I referenced above is, sure. But the odds are incredibly low, and if anything were to happen, the bank would be falling over itself to fix it and make reparations so that you dont sue for a whole crap ton more.

Is there a more secure and still free option that I have overlooked?

Opening up yet another checking account solely for accounts receivable and transfer to accounts payable would keep your financial records more transparent.

Also, banks are doing "money transfer by email" now, so I don't know how great that is for business transactions, but in that instance you're just giving out an email linked to a money receiving account instead of an actual account number.

Paypal is also a pretty good EFT middleman, but their business practices have gotten pretty shady in the past 5 years.

How can someone use the account number to withdraw money without my consent?

They can use your account number to game your banks phone support and try to phish their way into your account.

Banks have gotten very good at combating this, but theoretically with just the address he lives in, your name, and a bad bank phone rep, he could get into your business.

The account number would just be one more piece of information to lead with.

I have 1 savings and 3 checking accounts with the same bank. Would they be able to gain access to the other accounts?

Dependent on how incompetent the bad bank rep I referenced above is, sure. But the odds are incredibly low, and if anything were to happen, the bank would be falling over itself to fix it and make reparations so that you don't sue for a whole crap ton more.

Is there a more secure and still free option that I have overlooked?

Opening up yet another checking account solely for accounts receivable and transfer to accounts payable would keep your financial records more transparent.

Also, banks are doing "money transfer by email" now, so I don't know how great that is for business transactions, but in that instance you're just giving out an email linked to a money receiving account instead of an actual account number.

Paypal is also a pretty good EFT middleman, but their business practices have become shady in the past 5 years.