The english Wikipedia reports that the wheelbarrow was invented in Ancient Greece, around 400 BC. (source given: M. J. T. Lewis, p.470ff.)
The italian Wikipedia says that it was invented in China around 232 BC, and it was later exported to Europe. (no sources)
The french Wikipedia says that it was invented in South-East China around the first century BC, by a semi-legendary figure named Ko Yu. (source: Robert Temple, Le Génie de la Chine) The page is featured as "great article" or something equivalent.
I searched for -> when was the wheelbarrow invented <- and wiki.answers.com, which shows up as one of the first results, says that it was invented by a guy or gal.
Newyorkcarver http://www.newyorkcarver.com/inventions2.htm says that nobody knows for sure, but the Chinese are credited for the first wheelbarrow in 100 AD, and it was basically a box with a wheel underneath. A huge leap in a better design, however, finally made its appearance in Europe sometime in the 13th century.
When there are these results, how do you determine which "source" should be trusted more?