The risk is real if you are dealing with dodgy clients, but the solution IMHO is not to deal with dodgy clients. At least not unless you do so through an intermediary, with pay in advance, when providing content that cannot be used to damage you in any way.

I cannot see a situation where just not providing an SSN is a solution, and it puts you in a place of not having a matched set of payer/payee tax paperwork.