A question many patent attorneys get from many first time inventors is “How do I know my patent attorney will not steal my idea and patent it himself?”
Both the State Bars and the United States Patent Office have strict ethical requirements that govern the conduct of attorneys. These requirements require that attorneys maintain client information (your invention) in strict confidence. If an attorney were to disclose your invention either by filing a patent or telling someone else, then the attorney would be subject to disciplinary measures that may result in the attorney losing his/her bar licenses.
Another reason a patent attorney would not disclose your invention would be for reputational reasons. If a patent attorney were to disclose your invention, the attorney would be subject to a malpractice suit and/or bad reviews reflecting this on the internet. If you were to read reviews of a patent attorney questioning his loyalty to clients, you would likely not hire that attorney.
As a practical matter, I recommend potential clients fill out an invention disclosure form that is an overview of their invention and sending this disclosure form to themselves or a trusted associate of theirs. This creates a record of when the inventor invented their idea. If a patent attorney were to submit your idea or a similar idea to the patent office, this record would be used as evidence that the attorney did not create your invention.
As a matter of policy, client confidentiality is a guiding principal at Pierson Intellectual Property Law Firm.