A friend and I recently spent 3 days touring Bangkok with our personal tour guide Joker. He was completely flexible on changes to our our schedule and destinations. We changed our minds more than once and he was always very accommodating.
He is very knowledgeable about all the tourist destinations (including shopping) and even knows the quirky destinations that are off the beaten tourist track. He constantly looks out for your personal safety, speaks good English, and is a fun person to be around. I highly recommend Joker to be your Bangkok tour guide.