Writers who can do the work but don't have the degree probably just fake it on their resumes, and I'm quite sure the companies never check
While this may be true of some companies I make sure my writers provide their degree certs and transcripts, along with 3 pieces of academic writing. I do actually take foreign writers on ocassion but only if their writing is of sufficient quality. I find the easiest way to assess an ESL's writing skills is to look at their informal emails. This is far more reliable as of course they may in fact have paid for their academic essays!