QUES: There was once upon a time a tailor who had three sons and only one goat

correct the punctuation.

CORRECTED: There was once upon a time a tailor who had three sons, and only one goat.

QUES: They have heard that opportunism consists of a love for blocs and that is why they are against blocs

correct the punctuation.

CORRECTED: They have heard that opportunism consists of a love for blocs, and that is why they are against blocs.

QUES: Then our team of sports scientists serious athletes and service technicians of many years of experience evaluate the products of different categories

correct the punctuation.

CORRECTED:
Then our team of sports scientists, serious athletes, and service technicians of many years of experience evaluate the products of different categories.