The owner should bring all medical records as well. Have the horse prepared. Flexion tests require that the horse stand with a joint flexed and then trot off. The horse should be halter broke so that he is able to stand for the test and trot off when asked. Have yourself ready.
Someone needs to have shoes on that they can jog in during the flexion tests.
Someone, preferably the prospective buyer, should be ready to ride, and put the horse to his intended use. Here the vet can hunt for potential problems while working. Have the proper footing. The horse should be asked to move on a hard-packed area, where subtle lameness' will be revealed. A sandy arena alone is not acceptable, because it can hide potential problems.