As long as we're talking about the veracity of sources, this is pretty much my take on it.
If something comes from an actual interview that we can see or hear ourselves or an authorised or official transcript of an interview, a Buckingham Palace (or equivalent) statement or press release, or an official or otherwise authoritative biography, I think it's safe to assume that it's worth taking seriously. Doesn't mean it's necessarily true - I remember how Buckingham Palace was denying the relationship between Princess Anne and Mark Philips until five minutes before the engagement announcement - but at least it's authoritative (I suppose officially sanctioned bald-faced lies are at least authoritative
).
Transcripts of interviews or conversations have to be treated a bit carefully unless they've been approved by one of the sources; as Skydragon pointed out, the placement of a comma can be significant to the meaning, and the original interview or conversation wouldn't have had punctuation, so there's sometimes some guesswork involved. This is especially the case if the interview itself isn't available to watch or listen to.
Anything in a gossipy biography, article, or TV programme, or in an autobiography, should be treated with a certain amount of suspicion because the author is probably pushing an agenda. It never hurts to try and match information from this sort of book or article with something from an authoritative source. I think we're all familiar with the way that even supposedly authoritative TV documentaries can make fairly serious mistakes sometimes, so it's always worth taking a bit of time to fact-check. However, if one of these documentaries contains footage of interviews with people like Martin Charteris, Pamela Mountbatten, or Margaret Rhodes, the chances are that it's generally pretty believable. Doesn't hurt to remember that editing of interviews and other footage can give misleading impressions (such as the Annie Liebowitz incident in the trailer for the documentary), but if the information in these articles or documentaries is broadly in line with previous information, it's probably safe to take it seriously.
Second- or third-hand reports of conversations aren't the same thing as live interviews. I don't know how many times I've heard "Philip told Charles he could go back to his mistress after five years of marriage if he didn't want to stay with Diana" as though Prince Philip was on the record as having said this. When you probe a bit, it turns out that this is something that Diana told a friend, a friend told Andrew Morton, and Andrew Morton wrote in his book. "Andrew Morton said that someone told him that Diana said that Charles said that Philip said," or even the more true "Andrew Morton said that in one of the tapes passed to him by James Colthurst Diana said that Charles said that Philip said," is a very different thing from "Philip said." Same with this business of Camilla's "how about it?" opening gambit to Charles (and also, apparently, same with some of Wallis Simpson's early conversations with Edward); if these things are said in private and we hear about them in ways other than the royal (or whoever said them) confirming that they were in fact said, then they aren't authoritative statements. Doesn't mean they can't be used in TRF threads, but they shouldn't be given the same weight as a direct quote from the Dimbleby interview or the Panorama interview or the Queen's statement after Diana's death, to give a few examples.
Newspaper and TV reports of royal events are probably reliable, but reliability is increased if more than one independent source say the same thing. If half a dozen reports of a visit talk about an enthusiastic crowd greeting Camilla and one report talks about half a dozen sullen-looking people, the report that's been backed up by other reports is more likely to be true, even it it isn't saying what you might prefer to hear.
Stuff that's picked up from tabloid sources, with the "a close friend/someone close to/a member of the household told me" level of verification, should be taken with a massive pinch of salt. With these papers and magazines it pays to read very closely and with critical-thinking skills fully engaged, because some of these authors are masters at juxtaposing a fairly well-known fact, an urban legend, and a personal opinion in such a way that the existence of the fact appears to lend legitimacy to the rest of it.
Unfortunately Photoshopping isn't entirely unknown in photos accompanying royal stories. At least we have some pretty knowledgeable people here who'll know if Kate Middleton's head appears on someone else's body who happens to be having a wardrobe malfunction, or if Camilla has been Photoshopped to look ten years older (or younger), but if a photo looks unlikely for whatever reason, it may be because it's been tampered with.
Stuff that's posted at other forums or in blogs, where a person with no inside knowledge at all is taking it upon herself to claim to know the thought processes and motivations of people like Camilla, Kate, William, Charles, and Diana, should be dismissed as fabrication.
Buckingham Palace, and to a lesser extent Clarence House, tend to respond to most of these press allegations with silence. That doesn't mean they're tacitly admitting that the allegations are true.
I probably haven't covered anything, and feel free to disagree, but that's my opinion, for what it's worth.
If I recall, the quote had been misquoted, one comma out of place and the whole sentence changes, that is what happens to make the story more exciting. That is why I try to post a link, bearing in mind, the punctuation has been inserted by someone who decided to transcribe the phone call.
And your opinion seems to be worth taking note of!
