I heard this during a radio ad yesterday.

Problem:
The preposition “on” does not belong in this sentence.

Explanation:
The speaker was describing the sales technique of the company running the radio advertisement.

She could have been trying to simplify a longer sentence such as “He did not try to sell me on the idea of an expensive system.”.

Instead of simplifying it by removing “the idea of”, she made it more difficult to understand.

Or she could have been trying to sound more sophisticated by inserting “on” in a sentence that originally did not include it.

Instead, she made it more difficult to understand.

Unfortunately, it is becoming increasingly common to hear the preposition “on” inserted mistakenly but immediately or soon after verbs.

Solution:
“He did not try to sell me an expensive system.”