although it money shouldn't be decisive factor in making decisions, telling the client that fixing problems in a mix during mastering is costlier and also more compromising to the mix than having it done by the mixer and coming back again later to master it. give them some tips, let them hear other premastered projects snippets and make them feel comfortable that a higher grade mix is within reach. gives me a bit more spare time
, and generally makes the client a lot happier in the end.