It is well known in the angel community that it takes more than a person month of due diligence to have a reasonable prospect of a return on capital.

Anyone you want to work with over a decade or more will do tombstone due diligence on the past to ensure that its dead hand will not undermine the future.

At least as important is to assure themselves that the CEO has the capability to build the business and grow with it. As a founder it is in your best interests to have this done as if you were being hired to manage the money under very difficult and unforeseen circumstances. This is a case of an ounce of prevention. Have a look at the history of Google to see what is at stake for all.