Earlier this year a Nature paper reported the data below [black squares with error bars] for the spectrum of high-energy cosmic-ray electrons. The peak was interpreted as evidence for 500 GeV particles (dark matter) predicted by generalisations of the standard model that include extra dimensions.
However, more recent data [shown as red points] from NASA's Fermi Gamma-ray space telescope was recently published in PRL. The data has much better statistics and shows no peak. More details can be found here.
This is a good cautionary tale. There is no substitute for two or more independent experiments to test a hypothesis.
I don't think Ronald Reagan was a good U.S. president, but his signature phrase "Trust, but verify" has merits.