Sorry I don't do trademarks. Only trademark attorneys can file trademarks on behalf of clients. Most attorneys will not sign a NDA because their state bar rules don't allow them to be a counter party to their clients. In otherwords, your attorney should not sign an agreement with you such as an NDA that may put you against each other in court.
However, if someone is properly registered with the USPTO and their state bar (you can verify online), it is very unlikely they would risk their career to steal your trademark or idea so you can usually trust them.