Is the Carbon 14 Test Conclusive?

The ratio of the isotopes we have here on earth as a finger print to identify the nebula that our planet formed out of. You can use modern technology to change one isotope into another, but it's hard and expensive. If there's no ous reason why someone would want to change the isotope ratios in an object, it can still count as evidence that it didn't come from here. interstellar travel appears to be really hard. And that means that alien races would likely try to conserve energy as much as possible.