The short answer to this is, I do anything and everything that the mix requires in order to make it the best it can be. Many online mixing studios have different “mix packages” that range from simple level and panning all the way up to a full-service “professional mix.” With me, the only thing I offer is a top-of-the-line, full mix package that includes any technique that is required to make your mix sound the best it can be.
If the vocals need tuning, I’ll tune them. If the drums need timing fixes, I’ll fix them. At no extra charge, because it’s all part of the mix.
The only exception to this is if musical parts need to be added. That is really more of a production job, rather than mixing. So if you want an additional guitar part, or a keyboard line, etc., then please work that out and have it done before you send it to me.