at that point, you really need to pull the "im the professional" card.
they are hiring you to take high-quality photos of a subject specifically because they lack the skill or equipment to do so. so why are you listening to their unskilled suggestions for setting up your equipment?
outside of just people being cheap, a lot of people dont understand that you aren't buying a photo, but paying someone with the skills to take a good photo and then edit that photo to make it look even better.
a photo is cheap, but a person's time of setting up equipment, time of taking photos, and editing aren't. but because there things are things that a buyer doesn't see, they don't fully understand that they are paying for that as well. they see 20 for a picture and think, thats a lot i can take one on my phone for free, even if its of lesser quality.
actually just had a similar discussion with someone about the cost of custom knives.