The buyer with the intention to sell the flats at a good price to both residential flats as well as commercial , may give plenty of false assurances whereas he may not commit them in writing which clearly indicates that the builder is not honest.
Since you are aware of the commotions that usually takes place in a market place and are well aware of the nuisances due to markets below your flats, you opted to buy the flat.
Practically speaking, the authorities will not come to your rescue every time.
They may impose fine one or two times on the basis of complaint but they cannot direct the shop keepers to close down the business, the shop keepers may approach high court with a writ petition invoking the provisions and rights as provided in the constitution.
You may better avoid confrontation directly with the shop keepers to prevent unnecessary quarrels or revenge attitude by the shop keepers against you.
The next option before you is to sell this property and choose a calm and better residence elsewhere.
Even though the law is very well orchestrated to prevent such illegal activities of creating pollution and health hazards, when it comes for enforcement, the mighty is right on such issues, hence you may take a considered decision.