Tuk tuk drivers in Bangkok are notorious for taking tourists on shopping trips, usually over-priced suit shops and other shops that sell crap
Make sure you say "no shopping!" to the tuk tuk drivers and agree on a fare before you hop on (do this for taxis as well just in case)
When you're at major attractions (like the Grand Palace), ignore anyone who tells you the place is closed or you can't go in for whatever reason (like you're not dressed right). They're usually in cahoots with the tuk tuk drivers
We fell for this scam and wasted 3 hours on a "shopping" trip. When it was clear to the tuk tuk driver that we had no intention of buying anything, he got very angry and upset. Eventually dropping us off in the middle of nowhere and we had to figure out ourselves how to get back. Don't fall for this!