There’s a superb piece in The Chronicle of Higher Education, where Robert L Park offers the “Seven Warning Signs of Bogus Science”. He goes into detail on each one, but here’s a summary of the list:
1. The discoverer pitches the claim directly to the media.
2. The discoverer says that a powerful establishment is trying to suppress his or her work.
3. The scientific effect involved is always at the very limit of detection.
4. Evidence for a discovery is anecdotal
5. The discoverer says a belief is credible because it has endured for centuries.
6. The discoverer has worked in isolation.
7. The discoverer must propose new laws of nature to explain an observation.