Off the top of my head - The things we would look for are evidence of a SAS70 and/or CEFEX certification, where the checks and balances are, is the money held at a reputable custodian, how are the investments registered and how has responsibility for monitoring and selecting them, conflicts of interest, distribution and investment processes and procedures, how each entity in the turnkey approach is getting paid, who has access to be able to give instructions on the plan and to what discretionary extent, business continuity procedures, limitations of their contract, services to be provided in their contract, and so on. I do agree that it's very helpful to have a consultant in these situations though!
Mary Ann I will echo Evan's thoughts. You do not go to your doctor and perform your annual physical right, you let the professional. Same should apply here.
There are a few items that you as a plan administrator should be aware of, and evaluate periodically, and it is not only the financial stability of your 401(k) provider--especially if they offer bundled services.
1) Are there any conflicts of interest? 2) Are fees that are charged to the employees accounts reasonable & necessary? 3) Are the funds being offered in the plan the better ones out there?
Remember the fiduciary rules have changed recently, and lawsuits can be brought up against plan sponsors.
By finding the right financial advisor to do it for you.
I agree with Don. To expand on the fiduciary role, have them present on their fiduciary standards and processes and how their fiduciary system has helped clients mitigate regulatory risk in addition to investment risk. Asking for case studies or whitepapers can give you a clearer picture as well.