Does a real estate office deserve the full brokerage commission (2.5%) for describing the location of a villa, knowing that it did not undertake the usual marketing and mediation efforts, nor did it communicate with the owner or possess the property deed? And how much does the office actually deserve for this limited effort?

If the bank is the buyer and not you, then the articles of law do not apply to you unless the bank has appointed you as its agent. The real estate agent has the right to demand his commission from you. As for the seller, he is not obliged to pay anything to the agent because he did not agree with him. The agent's fee is subject to agreement, and since no agreement was reached, recourse is made to custom. If custom dictates a specific fee merely for describing the property, then you are obliged to pay it. It has been established that "what is known by custom is as if it were stipulated by condition."