I'd love to be wrong, but as others have already said, it smells fishy; this looks more like someone trying to get free images for his softcore porn website than anything related to an art gallery. Besides, shouldn't someone already in the business know what are the preferences of his customers? I would probably present him all images and decide together which ones to choose.
Just my two cents.
I appreciate the concern, but I've seen his website and there's no "softcore porn" there. And that's not even what pinup is.
Can we stop with the sky falling, and get back on topic?
Agree on his knowledge about customer tastes. I was planning to offer him just a handful of images to choose from, but fifteen is IMO too much. That's why this exercise. But I'm now leaning towards none, and to present him the final product when it's ready.