Good question which shall never be answered with any certainty. It is all personal taste and that is what custom work is all about.
I am not going to say I am the only guy offering the fresh out of a paint shop look in full gloss but I do get requests for it and am happy to oblige. there was a short period where two of my customers demanded nothing but that look and I did quite a bit of it. Awesome look if you are displaying your engine. Nice counterpoint to old and beat up if you are running it on a layout.
As far as what you are going to get without asking, light dirt applied in all vents and fans is the standard look for my pieces. If you do not want this you will need to tell me to skip it. Maybe this is going to be your only custom piece and everything else is off the shelf. You want it to match that look, that is fine. A little dirt even on otherwise clean engines adds a lot but you are the boss and I do what you want.
Heavy extreme weathering falls into an extra step category and will add the one price fits all charge of $20 extra to do more than standrad weathering.
Check out samples from top to bottom. Fresh out of paint shop look all in full gloss and spotless, to the "standard look" I do unless you tell me not to. On to the full out beat up and nasty look.
My last name is King, and like the burger joint with the same name, you get it your way when ordering from me!