Ok, now I can answer your question...lol!!!
First when buying it in a store, well, it has already been picked, processed and packaged without any thoughts of reverance...So in the past when I didn't have my own tobacco (I grow my own now-was a time living in the city that I couldn't), after I bought it, I said a blessing over the tobacco...that way I felt I had "cleansed" the tobacco...
Now on to picking the tobacco...It is the same when we take anything, my people when they were on a hunt or gathering herbs, food planted and ready for havest, always said a blessing of thanks to the Creator, usually there was a ritual done the night before havesting that all the people participated in...When in a hunt they would thank the beast for it's sacrifice and then take the meat...
Today, when I havest anything from gardens I say a blessing and thank the spirits the opportunity to recieve this and then havest it...
Hope this answers your question....