Just say no
For some reason, Hoa Lu has more pushy vendors than most place we've visited. It might have had something to do with timing, because when we visited the place, we were the only tourists there. A firm "no" usually does the trick, though we had to repeat that quite a few times. I enjoyed the scenery, but I got quite upset here at the locals. Maybe it would've been better if I hadn't been able to speak the language. There doesn't seem to be a public restroom here, so you'd have to use a paid toilet for around USD0.25.
At Tam Coc, there wasn't any annoying vendors, but there's a different setup. The only way to see it is by boat. So the arrangement is someone would accompany the person who row your boat to sell t-shirts, embroidery, souvenirs, etc. The rowers had to work hard for just a little money, so we felt obliged to purchase something, though we didn't have to. The goods didn't cost much at all and they were polite, so we felt pretty good.
Kim Giao---this one is found at temple of King Dinh---guide told me that long time ago people makes chopsticks from Kim Giao to proof poison in food---normally it is white but if it contact poison it will become brown or dark color.