If any employee shall receive less than the legal minimum wage, except as hereinbefore provided in RCW 49.12.110, said employee shall be entitled to recover in a civil action the full amount of the legal minimum wage as herein provided for, together with costs and attorney’s fees to be fixed by the court, notwithstanding any agreement to work for such lesser wage. In such action, however, the employer shall be credited with any wages which have been paid upon account.