Very good point.
I used to sell radio air time awhile back, and it's not rocket science.
Here's a perfect example of this.
Young's Jersy Dairy in Yellow Springs constantly called us wanting free public service announcements about thier bussiness. They would hold some stupid advent and want it advertised for free.
They would never buy actual air time from us, after they submiited another request for a psa, I called Young's owner.
I asked him if I came down, if I could get free ice cream. He seemed surprised, and said no. I asked him why not, he wanted us to promote his business for free.
Then I asked him again if he wanted to buy airtime. For some reason, this really pissed him off and he hung up.
I think story applies here as well.

Talking about TTS products is fine... making sales is not unless you are a vendor