This FindLaw article gives a sample retainer and contingency agreement for an injury case. This client Retainer Agreement is for ongoing service agreements between a client and consultant or contractor.Subject to the terms of this retainer agreement, in the event any bill from this firm remains unpaid beyond a 30-day period or, if in the judgment of this firm. What is a Retainer Agreement? A retainer agreement is a work-for-hire legal document or a service contract between a company or an individual and a client. This agreement for legal representation is between, AGENCY NAME, and CLIENT(S) NAME(S).