Bad Manners?

Is it bad manners to not take the advice of somebody behind a counter?

I was buying some cough lollies, and after making my considered choice, placed them on the counter. The guy looks at me straight in the eye, and gruffly says, "THESE are much better", gesturing to the high falootin' twice-the-price option. I paused, and ummed and ahhed (I am generally very easily swayed), but thought, no, stick to your guns, Benny boy. So out I went, with my lesser cough lollies, with a stern glare from the guy behind the counter.

Had this taken place in a chemist, I may have heeded his advice, but this was a petrol station. Since when did servo guys give pharmaceutical advice?