These sales (1)/ led us to think that (2)/ there is not much of a market (3)/ for this kind of product (4)

Here, error lies in part (2) of the given sentence. In it use of ’led’ is incorrect instead it should be ’lead’ because the given sentence is in present tense and ’led’ is past participle of ’lead’. Hence, the correct answer choice would be option 1.