Bob,
What happened to the client? Was the client actually arrested or charged with fraud? If the client was NOT charged with fraud, we should ignore the fact that the client is trying to commit fraud. Otherwise, you risk fooling yourself into thinking you have the Amazing Ability to detect a fraud.
Simple Possibilities:
(1) If client is indeed charged and sentenced for fraud. It is logical to think the fraudster had chosen an SSN that is near to his own real SSN. Just in case the attempted fraud is discovered, s/he could always claim it is a mistake.
(2) If the client is honest and not sentenced as a fraudster. We should give him the benefit of the doubt that it is just a genuine mistake. Unless he is totally deranged, we could reasonably expect the SSN he gave to be close to his real SSN.
Let me guess... this client was NOT charged for fraud.