How to decide which is the correct scientific name for a particular species
When it comes to plants and animals, common names clearly differ from region to region.

A first effort to univocally classify them was done in the 16th century by Carl Linnæus (see my answer to this question for some historical background).

The nomenclature of plants is governed by the International Code of Nomenclature for algae, fungi, and plants (ICN), and for animals from the International Code of Zoological Nomenclature (ICZN).

The fact that there are rules, however, does not imply that names are conserved over time, nor that there is a rule for everything!

As time goes by rules change, certain species may be assimilated by others, or a certain subspecies will separate and become its own, and at times name changing proposals even raise havoc in the scientific community.

In summary, it is important to remember that taxonomy poses rules that are there to facilitate talking about science. Those are not absolute rules, sometimes they are arbitrary, and therefore for certain species there is no univocal name (and surely there is no correct name).