Or, "You can have this great product free, as long as you sign up for a month's trial of one of our sponsors' products. Cancel at any time." knowing many people will forget to cancel & wind up paying.
Why did infinity314 get voted down?
He's right; "Freemium" is a real thing.
When Avast Antivirus gives away the basic download for free, but then there's a popup that says, "y'know... for a small fee, you could have this way more awesome version..."
That's "Freemium."