Why would someone want to be the "go-to-guy" for a client that's refusing to pay an invoice of $780? I can understand the referrals just because it's YC. But, i

Why would someone want to be the "go-to-guy" for a client that's refusing to pay an invoice of $780? I can understand the referrals just because it's YC. But, in general, I doubt designers go around asking clients that refuse to pay for referrals.