If a government or a company publish their data as Open Data, you don't have a (theoretical) reason to not trust their data.
But what happens when the data is a result of crowdsourcing. Can we trust them with the same way we trust the data from official publishers? Is there any way to evaluate them? Can we use them on research or contests about Open Data?
A recent example: A local municipality has published a dataset of points of interest. Wikimapia has also a dataset for the same area but it is bigger and with more details than the official one. If I want to create an application, I can choose the dataset from the municipality and I will have an official "stamp" for the data and better "social acceptance", but my application will be misfunctioned. Or I can choose the "unofficial" dataset from crowdsourcing and create an application without the official "stamp".