How Do You Explain Slow Shutter / Ghosting To Clients?

Most of our clients don't question it, nor do we ask generally. We make the adjustments based on what we feel will provide the best image quality in day/night scenes and usually is on point with the customer's expectations. We will sometimes get some feedback to make minor adjustments here and there.

We normally don't even need to adjust too much unless it's a specialty application like LPR or FR. 

I would do just what you suggest, present 4 or 5 snapshots at different shutter speeds.  Start at 1/30s, which I think should be the absolute maximum, then 1/60s, 1/120s, 1/200s, and then maybe 1/500s only in good light.  Pick something moving at a fixed speed so the comparison is easy.  Obviously at 1/500s whatever is moving should appear perfectly still and sharp, while at 1/30s you see substantial blur.  Someone walking fast might work. 

I think seeing a softball "mush" might be a bit beyond most security camera needs.  For the rare application, maybe try 1/1000s or even faster.

I was referring more to the differences in camera quality and price points/value. I wouldn't ask the client what shutter speed they want. The few times we played around with shutter speed, to reduce motion blur, the image got darker, as expected.

From some of the testing I have seen here, some cameras will do better at faster shutter speeds and low light. Of course that usually means a more expensive camera.

I was thinking more of like, here Mr/Mrs customer are 6 snapshots from 3 cameras. the first 3 are at default settings, and the image is bright but you get blur. Here are the same 3 cameras, with reduced blur, and you can see the difference in darkness. The worst camera costs $100, and the best one costs $600. What would you like?