Why did people buy thomas beckets blood?

People bought Thomas Becket's blood due to its association with his martyrdom and the belief in its miraculous powers. Following his murder in 1170, Becket became a symbol of resistance against royal authority, and his blood was thought to possess healing properties. Pilgrims sought relics like his blood at Canterbury Cathedral to seek divine favor, healing, or protection, reflecting the medieval belief in the sanctity and power of saints. This practice also illustrated the intertwining of religion, commerce, and devotion in medieval society.