Under the consumption-based model for asset pricing, different people will have different prices because of their different utility functions.
What is the force that make the law of one price hold?
You might say that it is a result of no arbitrage, but Kerry Back states in his book Asset Pricing and Portfolio Choice Theory states the following
The law of one price is a weaker condition than absence of arbitrage opportunities: It is implied by the absence of arbitrage opportunities, but it does not imply the absence of arbitrage opportunities.
Based on this statement, absence of arbitrage is a stronger condition; the law of one price should hold even there is arbitrage in the market. So What is the force that make the law of one price hold?