Tire Valve problems of the 1997 Toyota Camry

On 3/21/07, I purchased 4 new tires from merchants tire in williamsburg va which included new valve stems. Immediately after I drove away from the service facility, my rf tire was flat. After further examination by the service writer at merchants, it was determined that a leak had developed from a cut at the bottom of the valve stem. It was the service writers theory that the valve stem was not replaced during the tire service. The valve stem was replaced and no problems occurred until the following year. On 3/11/08, I complained to the same facility about another problem with a cut valve stem but no leakage occurred. Prompt replacement was effected on request and as of this date, I have not noticed any further problems.