One of my first jobs in high school was being a product demonstrator at Costco.  Every week the product would change - frozen pizza, cake, granola bars and even a mop.  I didn't have to 'push' the product, I just had to cook the food and put it out in small sample cups or just demonstrate how to use the product should someone ask.  Occassionally I would ask if someone wanted to have a taste or see how something worked, but very rarely.  Here's why:

1. People, LOTS of people love anything that's free.  Especially when there is no risk involved or you don't have to provide your name. 
2. People get hungry when they are shopping.  Have you ever opened a bag of chips or can of pop while shopping and then paid for the product when checking out?
3. Many people don't steer away from brands or products they are familiar with and know how to use or know what it tastes like.  But, should they have the opportunity to try something without having to buy it...they'll take it.  AND, if they like it more than what they already buy...(don't forget to give a coupon!)
4. People like demonstrations.  They need to know how easy it is to cook or use.  'Yes, just pop it in the microwave!'