Term for Successful Sale after Demoing Product

I believe there is a business term for such an event, but I can't recall what it is.

An example would be a vacuum salesman showing a prospective buyer how a vacuum works, and the buyer ends up buying one.

Presentation based sales are a type of Promotional sales technique. I am not sure if there is a definitive answer that clearly applies to your specific sense. However, there are a number of more generic terms that could apply just fine to your meaning, even if they aren't "official" words specific to your need.

For example, you could call a sale made by demonstration a "Demonstration [Sale/Close]"; "Presentation Based [Sale/Close]"; slang: "Demo Close"; Etc.

More generically "Promotional Close"; or just "Close", "Closed-won"; Etc.

Here is a list of business sales terms that might be helpful. See https://saleshood.com/blog/sales-business-terminology/ for definitions of the above example words.