What is the difference between 'our product is in the market' and 'our product is on the market'? And WHY?
It is most common to hear the phrase 'our product is on the market' because the market (in general) is unbounded. If you were to place your product for sale in only one market place then it would be proper to say 'our product is in the market' because it would mean a specific "bounded" market. For more about using prepositions of place see this link: Prepositions of Location: At, In, On