Interesting... never thought of it this way. However, most of my customers are over 60, running Windows 7, resistant to change, and not a lot of extra money to spend . So if there is an option to keep the familiar system (Win 7) vs. going to Windows 10 they would rather keep the system they have. So then they pick the cheaper option.
Ashamed to admit this, but really never thought of installing a smaller SSD than the original HD. (self-flagellation begins and will continue for a while....). Also like your idea of a refund if they're not satisfied.
What do you do with a Win 7 system where you've replaced the HD with a smaller SSD, and the SSD fails for some reason. How do you get Win 7 reinstalled? If you get the Dell installation media, it will only work with the size of drives originally available on that system when it shipped from the factory.
Never had an SSD fail yet. A good backup solution would work and should be used for either type drive. I don't understand your media question....a drive is a drive is a drive. If it installs on a platter drive it should install on an SSD.
Also, what software do you use to shrink the Win 7 system so it will fit on a smaller drive? Do you use what comes with the SSD, or other software that you like better?
I use Acronis mostly, but their are others also.