To then draw a conclusion that this amount means that the specimen is umpteen million years old involves interpretation. This interpretation is based on assumptions. No, such an interpretation would be based on the ignorance involved in using the wrong tool to do the job or in plain old gross incompetence. The principle of radiometric dating, however, is simple and reliable. It is based upon the fundamental laws of radioactive decay.
Radioactive elements decay into other elements at a known rate.
Multiple dating techniques exist and can be used to cross-check each other. Creationists try to attack radiometric dating techniques by advancing a mangling of the process of radioactive decay. Finally, since you can't predict how it will proceed, you can't extrapolate from observations of its progress, either. Therefore, they say, radiometric dating cannot be used to age-date samples with any degree of reliability. However, the randomness is in which particular atom of the radioactive element will decay at any given point in time.