Its not a secret that locals love to do their fruit, vegetable and meat/seafood shopping in fresh markets. Not everyone wants to go to big super/hyper markets like Tesco Lotus or Big C and hassle with transportation when there is fresh market probably just around the corner. Pricewise, fresh markets are normally beating super markets as well. And one in the Khlong Toei beats them all. It is without a doubt the cheapest and best fresh market in the city.
This market aint for everyone though. Its busy, people shouting on trying to get your attention with their promotions and very hot. It is naturally outside market and only umbrellas next to the shops are saving you from burning hot sun of Thailand. But this is how us locals live in Thailand. Visiting fresh markets like this one is just another shopping trip for us.
Khlong Toei market is pretty much open 24/7. Some shops are open only during the day time (roughly 7am-8pm) so thats the best time to go there.
Not everything is for eating though. There are living turtles and frogs for sale as well and they are for religious purposes. It is Buddhist ritual for releasing such animals to freedom. This is believed to build good Karma for the people following this ritual.
Location wise, Khlong Toei market is easiest to reach via MRT. Closest stop is Queen Sirikit convention centre and its within walking distance from the market. Here is the map of the location for your convenience. https://goo.gl/maps/W6Saqt7q8QjASpQe9