During the WIP phase I will send the sketch and during this time i'm more than happy to make changes if needed, however if the sketch becomes approved and I continue with lineart as well as color I am less willing to make major changes, in most cases I would prefer not to without additional fee.
If the reference given is extremely vague I will need additional details and specifications on important aspects of the character drawn or else I can't guarantee I will get it right, and i'd prefer to avoid unnecessary efforts to try and figure out what it is you're wanting.
I tend to be very busy so the times in which I can complete a commission vary all the time, if time is an issue at all please state so in your commission so I can be sure to finish it in time or let you know if I will be unable to meet the time limits