hi there
its a difficult one, if you were in the area, with machine ready to rock and roll then great,
but if you travelled especially to do that job, then maybe not...
the argument is
you have taken xx amount for the day or week, and therefore this bit of free marketting may pay dividends in the future.
if you have reaped rewards from this client in the past and you know they are good jobs then, why not. proves the good samiratan still roams the earth in some form or another.
regards
martin