When customers believe that they have bought a product, they congratulate themselves on their good judgment.
When customers believe they were sold a product they often grouse about either their bad judgment or the sales person or both.
Buyers brag to their friends about either their great choice, about the sales experience or both; referrals are often the result.
The second category of customer may be either complacent or unhappy. In either case referrals are not likely to result.