Final answer:
The Tristram's Landing v. Wait case established the precedent for when a real estate agent is entitled to commission in Massachusetts.
Step-by-step explanation:
The case establishing when a real estate agent is entitled to his or her commission in Massachusetts is Tristram's Landing v. Wait.
This case set the precedent for determining when a real estate agent earns a commission, which typically occurs once the agent has performed the contractual duties and brought about a transaction between a buyer and seller.
It's important for agents operating within Massachusetts to be aware of this ruling, as it directly impacts their entitlements to commission based on their role in real estate transactions.