Can anyone tell me the rights of a sole proprietor when it comes to the way they handle the account? If they are John Doe DBA ABC plumbing can they cash a check payable to ABC plumbing or must they deposit that check and write a check to cash? And if they can cash the check, why?

It's a matter of state law and bank policy. Some banks allow it, while others do not.

Sole proprietorships, at least in Wisconsin, are not recognized as separate legal entities.

That is why, even though we set them up as business accounts, in some ways we allow them to be treated more like personal accounts. Cashing checks is one of those ways.

Just to be clear. No one has a "right" to cash a check unless it's drawn on the bank being asked to cash it. Banks accommodate their customers by cashing checks from time to time, but it's not because the law requires it.

Your bank can establish its own policy based on its own risk assessments and business model. Many banks have found it easier to say that they will not cash checks payable to a business regardless of the legal form in which the business is operated. Their reasoning: It can be a challenge to determine whether a given business is operated as a sole proprietorship or by a partnership, LLC, corporation, etc., and they don't want their tellers having to understand whether ABC Plumbing is a sole proprietorship or not.

As Ken Golliher has repeated in these Threads many times: a sole proprietor is in a position to request that his/her customers make checks payable in the business name or to him/her personally. If he/she wants to be able to cash checks received from customers, those checks should be payable to the proprietor, personally.