The money-back guarantee applies to the 16oz trial package. When you have determined this product meets your needs, this size or the 8-liter twin pack is the smart choice. This unique product works on carpets, upholstery, mattresses, leather, drapes, floors (wood, cement, terrazzo), walls, kennels, etc. Manufactured since 1978, you won't find a better product that will eliminate urine odors and stains. Urine-Erase(r) uses a two-step process. First a dry enzyme powder is mixed fresh with water. This solution is poured onto the porous surface and breaks down urine so it will react with the bottle of solution (gentle peroxide) that is applied approximately 8 hours after the enzyme. Stains and odors disappear "Poof" like magic within hours after the second step. A reaction takes place to break down the urine into water and oxygen. Use of Urine-Erase is ideal where indoor air quality is of concern. Note: physically damaged or bleached fabric cannot be repaired by any product.