Joan represents the buyer, Carlton, while Reggie represents the sellers, Zeb and Teresa Martin. Carlton's Great Aunt Matilda has agreed to pay any part of Joan's commission not covered by the sellers. Teresa's father, Teddy, has agreed to pay half of the sales commission owed to the listing agent. Which statement is true?

Based on the information provided, the following statement is true: Carlton, the buyer, will have an obligation to pay a part of Joan's commission only if the sellers, Zeb and Teresa Martin, do not cover the full amount of the commission. Since Great Aunt Matilda has agreed to pay any part of Joan's commission not covered by the sellers, it means that between the sellers and Great Aunt Matilda, Joan's commission will be fully paid. Therefore, Carlton doesn't have any direct responsibility to pay Joan unless the agreement with Great Aunt Matilda fails to materialize.

Furthermore, the statement that Teresa's father, Teddy, has agreed to pay half of the sales commission owed to the listing agent (presumably Reggie) does not impact the buyer Carlton directly but rather affects the financial arrangement between the sellers and their respective agents.