Hey,
no one started on maximum level as 3D-artist. So, I hope you are not too frustrated because that client imagines something different.
Look at the early work of the best 3D-artists on the market... EACH of them started with quite modest outcome.
In older times, 3D-render softs were quite bad, ineffective and slow. Now, thanks God, things have changed, so literally everyone has the chance to become a reasonable 3D-artist if he/she has at least a minimum of artistic talent.
If you are eager to learn from other colleagues, study images & photos with an "analytic eye", talk with photographers about their approach, read a lot of 3D threads - and most of all - try to develop an own style while never thinking "oh, now I'm great".
Then I guarantee you that you will reach a high level.
However, I don't want to sound like Mr. Over-teacher... :)))
Technically you are already an a solid path.
