Is the effort worthwhile for someone who informed me of the availability of land for sale, and then I searched for its owner and details myself?

The person who informed you about the availability of land for sale with a specific family, without providing additional information, does not deserve the commission (brokerage fee), even if he led you to the landowner, unless an agreement on the fee was made beforehand. However, if he was a broker and exerted effort that would entitle him to a fee according to the custom of brokers, then he is entitled to a customary fee (ujrat al-mithl) according to the majority of scholars, contrary to the Shafi'is.