According to their religion, the souls of lamas, or priests, are frequently reborn as Lhasa Apsos just before they are reborn as humans.
Lhasa Apsos were often given as gifts in Tibet. If you received a Lhasa as a gift, you could consider it a sign of good fortune.
The spiritual leader of Tibet, the Dalai Lama, even gave Lhasa Apsos to the emperor of China many centuries ago. Though they were often gifted, Lhasa Apsos were hardly ever sold.