The first piece of advice is also the easiest:
"Follow your nose and your gut," Casablanca tells me. "If it smells bad, it probably is."
More specifically, he says, believable evidence usually comes in bunches; photos, snubs and absences alone don't say so much as a photo and a snub and an absence.
First, Jessica Biel didn't accompany Justin Timberlake to the Emmys. That alone could have been explained, but pair that absence with weeks of rocky-romance reports and a recent photograph of the two of them refusing to look at each other and looking miserable, and it comes as no shock that Casablanca is now reporting the pair is "off and on" right now.
Sean Penn snubbed his wife during his Oscar acceptance speech, and they also looked miserable together on the red carpet. When the reports came in that they were done, it was all that much more believable.
Conversely, check out Brad and Angelina. Tabloids have them breaking up every other day. But you don't see miserable photos, public snubs or a slew of events where one appears and the other doesn't. The evidence doesn't add up. Ditto with Stephen Moyer, who showed up at the Emmys without fiancé and True Blood costar Anna Paquin. The absence came with no other signals that something might be wrong, so suspecting a breakup there doesn't make so much sense.
The final clue doesn't always work, but it's a good general indicator, and that's geography.
For weeks before Angelina announced her split with then husband Billy Bob Thornton, the two had not been seen together, photographed together or even spotted within the same 10-mile radius of each other. Reports had Angelina in one city, Billy Bob in another, over and over and over again.
Sure, movie stars have to jet all over the world for their jobs, but loving couples still manage to meet up via private jet once every so often.
See who split, and badly, in our Bitter Matrimony gallery.