In my opinion it's not an option, it should be done for Interior Only, Exterior Only, or both.
You'll have to dry door jams after exterior washing, so you can clean it as well.
For interior, they are the 'border' of your artwork. It can't look dirty.
It'll be just an extra spray of water, an extra towel pass and an extra spray of quick wax... Automatically charge $5-$10 more than the concurrence and let clear there are no optionals, everything is included. Your price is higher, but they get what they pay for.
What I do generally (someone already posted here) is clean up on maintenance, but only do a full detail when charging for it. Full detail includes everything needed, from claying, polishing, degreasing hinges, scratch removal or masking and dedicated wax/sealant application...
This may be an 'optional' for discussing further with customer.
Another important issue I've read here, is about the choice of the client. In my opinion, client have to chose you. You must be able to chose the rest for him.
I say this because many of my clients wants a scratch-less, shiny and clean car, windows, wheels, but they don't know how to do it. If you know, you should get the responsibility for them, and be sure to always make the right decision.
They will trust you and that's what's important. If they knew better, they should be doing the work instead of letting you do for them.
In example, I never let my client chose wash + wax (when very contaminated and harsh) without a claying and at least 1 cleansing polish step. They don't know the importance of it, so for them it may be optional. For me, it's obligatory (at least when 1st time servicing the car). It's up to you educate your customers, chose the best for them, and adequate your service to client expectations and money invested.
Sorry if looks confuse, but I'm willing to entertain Flash Gordon!
Kind Regards.
rops: