The truffle must come covered with fresh ground, a good sign that the truffle is fresh from the under ground. However some truffle vendors take some fresh ground and “up the weight” by forcing fresh ground into the truffles crevasses. In the old days I would see little stones added with mud to increase the weight.
The cleaning is simple and requires water and a tooth-brush. You simply use running water and the tooth-brush, maintaining one direction when brushing to remove the ground. Do not place the truffle under the water, and keep the toothbrush clean as you brush by washing it frequently under the running water.
The entire process should be finished in a few minutes and the truffle dabbed with odorless paper towel to get a fresh and dry look. Remember its living and be gentle and take extra care to avoid damaging the truffles surface.