I think the 30 rule makes sense. If you live in Los Angeles and you are shopping a bank in San Diego, I can see where you would get funny looks.
When I was a newbie shopper, I went into a bank 28 miles from my town and the banker said, "You live in XXXX, why are you in XXXX?" I HAD to think fast. I said, "Oh. (the only think I could think of) I will be moving in this area in 2 months and I was just checking out the area and the bank."