We recently visited Bangkok for a 3 night stay, none of us had been there previously, on recommendation from friends who been there in 2016, we booked a guide through, Your Thai Guide.
Their website is so easy to navigate, we made contact through their website, we received a very prompt response, they were so helpful and made the whole process simple. Whilst we had ideas of what to visit, their help and understanding helped us get the most from our limited time in an amazing city.
Our guide on day 1 was Jean, a very knowledgeable guide, we had an excellent day, the guide company had also booked us an evening dinner cruise on a converted rice barge, the arrangements made for us worked like clockwork.
Day 2 we had Nina as our guide, she was great, again, very knowledgeable but also very personable.
The only reason we had differing guides was because we left it late to book, my tip would be, book as soon as possible, everyone we had contact with at Your Thai Guide was very prompt, they could not have been more helpful, we would certainly use them if (when) we are heading back to Bangkok.