Handbag Harresment

I had a bad experience at Shoprite today.I was there to purchase some goods. When you leave the store there are security guards who check your slip for the goods purchased.The security guard then proceeded to want to search my personal handbag.She was quite eager to do it.She told my that my handbag is full of items that sell and that if those items were not sealed I would have a problem. I did not understand this as this is my personal handbag.This is the only store I have walked into and been harressed like this.Since when is it a crime to carry ones personal handbag into a store.My handbag had R500 cash in it, my ID book,dentyne, vaseline, gaviscone, an open packet of peanuts, diary, my clinic card, two cellphonnes and small umbrella. I am upset as it is not written anywhere that customers are not permitted to carry their personal handbags into the store.I could not leave my handbag at the parcel counter as there are items in my bag are difficult to replace.Is there a law that does not permit paying customers from carrying their personal handbags into the store? If so, why do they not write such things at the door of the store so that I know that my money is not needed by them.