[Ifeffit] distinguishing between actual shells and artifacts

Dear all, I am currently fitting first and second shells with Zn-O and Zn-Zn paths,respectively. I get second shell features that could be fit quite well, but I am not certain if they are actually second shell features or possibly artifacts. For some samples I get second shell features that I know should not be present. What criteria would you use to distinguish between artifacts and actual shells? Your assistance is appreciated. Hashem Stietiya Louisiana State University