I would be upset as well.  If it were me, I'd politely give him the option to send the search on the terms agreed or cancel the order.  Very unfortunate.  I understand being skeptical these days and the concern for ever getting paid.  However, I always give a new client the benefit of the doubt and we extend our usual NET30 terms. 

I agree with you - if you don't tell the client that you expect payment before you return the search, it is just rude and unprofessional to hold it hostage for pre-payment.