Our stores put out trays of fruit, crackers, dips, cold cuts, etc for people to taste. If it looks appealing and reasonably sanitary I try it.
I have had grocery managers encourage me to try the grapes, cherries, and other similar produce in the local stores, so I do. I got no problem trying *one* grape to see if they are sweet or sour so I know whether to buy them. The store managers here apparently don't have a problem with it either. It's not like I'm walking around eating the entire bag.
Now, I don't bite apples or rip open oranges, or open other sealed packaged items in the store... except sometimes for scented items. Yeah, I'll open perfume if it is not safety sealed. I never mangle the box and you'd never know I had a sniff at it. I can usually smell enough of it without spraying anything, so I'm not "using" the product. I open liquid detergent sometimes too to see if it is something I want on my clothes. Perfumes give me a headache so I have to be careful about them.