Quote by Sir-Shredalot
As luthiers do you reckon that natural finishes enhance tone, sustain or anything else?

Not really enough to hear by ear, but it is often thought that a natural finish (which is far thinner than multiple layers of sealer, primer, paint and lacquer) would be a benefit in that department.
I'm assuming by "natural" you mean an oil? Because shellac is all natural as well, but with far different properties than oil.

But I agree with everyone else, I don't think it affects the tone, or at least not enough to really notice.