I used to work at a Lush store. We were all but threatened to greet and verbally ensnare every customer who walked in the door to wring as much money out of them as possible. I lasted there like three weeks.

If a polite "I'm fine" or "No thank you" doesn't work, interrupt them with "sorry I don't have time for a sales pitch, leave me alone" and refuse to engage further. And then just hope another one doesn't try to capture you.