This is a step which is often neglected because it does take a lot of time to verify data sources. However, if you selected information from the “Validated” sources i.e. government, public organizations such as WHO, UN or traditional media (Reuters, CNN etc), your source of data will not be disputed.
However, there are plenty of user submitted databases out there which are very difficult to ascertain the validity. You sometimes would have to contact the owner of the data set to double verify the existence and methodology in which the data has been collected, e.g. graph on the height and weight of celebrities. When was the data taken? Were they all measured at the same time? Who or how did the data get collected?
You will also notice that going through 2 different sources of data for e.g. population/health measures in Kenya for 2011 will get you different numbers with the same metrics. In this case, which one do you pick? Always try to reference from a reputable source of data to avoid any conflict in the future. Always leave a reference to the URL or place you obtained the data from.