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As to the claim against the owner or shareholder for the corporate debt, which they signed for and paid out of a personal check, collection by you, would be based on the legal theory of 'alter ego', and it differs from the shareholder's personal liability as an individual.
Under the alter ego theory, a shareholder can be liable for a corporation's debt upon a showing of certain circumstances, which include the 'personal' use of corporate assets, the mixing (or 'commingling') of personal and corporate assets, or the undercapitalization of the corporation and using their own money to pay the corporate debts. This is how you would be able to sue the owner in small claims court, and in a small business setting, this is often successful because individuals in small businesses fail to maintain the separation between themselves as an individual and their corporation, leading to potential liability as an “alter ego”.
If they did indeed pay you initially with personal checks then they would be comingling the debts and paying with personal assets, thereby allowing them to be named personally for the debts.
I hope this helps.
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