I get a lot of inquiries asking simply "how much for...".
My answer is "it depends on the level of service you want". I lose some with that answer.
My approach is to answer with a very open ended question. You really can't answer it because as you noted, you have no idea other than price what the concerns are. I always state; "tell me about the vehicle, age, past care and what the top 3 concerns are or what they are looking to accomplish by getting it detailed." From there you can drill down by asking a clarifying question such as "so if heard you right.....blah, blah, these are your top concerns; but are there any others and what would be your
main goal to have accomplished"
Then you can talk about if they were presented with several options.....describe your packages, etc. which one sounds most likely to meet their needs? Have them answer as it's their car and you're not there to overcome their objections or hurdles, you have to get them to do that.
I do then go into how their needs and desires are impacted by the size and type of vehicle, services needed based on their comments and the options around not just the package that they described meeting their needs best but I also go up a package level and down one too to provide them an opportunity to spend more and see their reaction and also a way to save face and money should they get some sticker shock. It's also part of the reason I price out my coatings and LSP's such as wheel and trim coatings ala-cart. It allows for them to better understand how things are put together, offers more options and again, helps them feel more comfortable making their own decisions about what I'm going to do for them vs me pitching what i think.
Thus the answer is always let the customer lead the conversation and look at things through their eyes not yours. That includes upon inspection and pricing. I say inspection as when I do mine, panel by panel, I have them provide ALL the answer. Here's an example. As we walk around the vehicle, I'll find the panel I think needs the most addressed and start there. In this case it was a door. I start by stating " so as we walk around your car, I'm going to ask a series of questions to further clarify your desires while at the same time providing you a "cursory" ( as I do two inspections, this is the first ) view of concerns I'm finding."
On this door I would ask if anything jumps out to them and what they want addressed and perhaps like to see. ffwd, I walk them through by asking questions, THEM telling ME about the scratch, the marring/swirls, oxidation and dullness and not only if and how they may have occurred but also what they would like to see once completed. Part of this is not only helping address your initial question about "how much" but also forms the basis and story behind any damage found. I hope that makes sense.
Sorry for the VERY long answer, but it's an important topic not only from a pricing and sales perspective but most importantly a CYA perspective for ALL vehicles you touch. My wife is an attorney and wrote my intake documents thus I'm inclined to perhaps make a video about this. Hmmmm....