Malls and stores are privately owned establishments with their own rules. Moreover, most places have laws that make the establishment liable if someone is filmed without their consent (ae: someone walks through your frame).

If you want to blog on someone's private property (Mall/Walmart etc ...), call the manager ahead of time. Tell them what you are blogging about, have copies of "release to appear in media without compensation" forms for anyone who your camera catches in frame (especially anyone you talk to).

If you are not disparaging their business, they will likely arrange a time and date that you can film.