Which of the Following Is Not True About Reciprocity

Which of the following is not true about reciprocity?

A) Reciprocity is a "fact of life" in business and should be embraced
B) Reciprocity exists when supply managers give preference to suppliers that are also customers
C) It is entirely legal to buy from one's customers at fair market prices, without economic threat, and without the intent of restricting competition
D) Reciprocity can become illegal when the activity restricts competition and trade
E) Reciprocity does not follow sound principles of buying and selling