We mean it when we say 100% Guaranteed. That does not mean we are perfect. (Even though we are trying to be.) Brand-new cartridges fail 2-3% of the time. Our failure rate is very comparable. If you have ANY problems with your cartridges not working properly, PLEASE call us. In many cases there is a simple problem that we can quickly solve for you over the phone. Or, you are always welcome to bring the cartridge back to us for free troubleshooting and testing. If we cannot quickly fix the problem, we will replace the cartridge or give you a full refund without a hassle.