I was involved recently in a demo of a product that a vendor was trying to sell to our firm. I won't identify the product or vendor, because this is not about the product itself. The vendor did two things that did more harm than good.
The first problem was the vendor's approach. They were quite proud of the product, and launched directly into its advanced and cutting edge features. But they ignored the basics. So anyone observing the demo who was skeptical of the product in the first place, or not comfortable with change, or felt the cutting edge features were not necessary would be turned off right from the start.
A much more effective approach would have been to start with: "Our product has some advanced features that can make your practice easier and more efficient, but let's start with the basic functions to show how easy it is to use every day."
The second problem was that the demo was done in part by a person who used their computer to remotely control a second computer that contained the software being demoed. That technology works, but is never as efficient as using the computer directly. So delays and glitches caused by the remote aspect are perceived to be problems with the product.