Just because there's a potential conflict of interest doesn't mean they're lying. I think this heuristic will quickly lead you astray if you rely on it too heavily.
Here is the same argument, substituted with different groups:
- Do you trust climate scientists, when their prestige is tied to how important their field is?
- Do you trust the science on vaccines, when the public health system relies on people's willingness to be vaccinated?
- Do you trust that Obama isn't lying about being an American, given that was running for President?
- Do you trust yourself, given that psychological research shows that data that contradicts a strong belief tends to reinforce that belief?
If you're going to call someone or some group a liar, I think it takes a lot more evidence than just 'they might have a plausible incentive to lie'.
To answer your question though, I have several technical concerns about how CPI inflation is calculated, but I definitely don't think it's due to someone actively deciding to fudge the figures.
The 2nd sentence was just a rhetorical point designed to nudge people into having some doubt about the statistic. I myself came to that conclusion long before appreciating its effect on the government budget, from watching the CPI and what I believed to be "true inflation" starting in the dreadful '70s (yep, I remember Nixon's wage and price controls), when I believe it was a lot more honest, say at least through a good part of the '80s.
Your subpoints aren't quite all the same, a good Upton Sinclair quote that's been bandied about lately "It is difficult to get a man to understand something, when his salary depends upon his not understanding it!", so e.g. #2 doesn't apply, the public health system doesn't make much money at all on vaccinations, that's more of a True Believer thing. See e.g. Governor Gardasil.
And I tried real hard in the 1968-80 period, 2nd grade through first year of college, and of course beyond, to seek out the truth at all costs, having decided at the end of 1st grade that science was my calling. And I think I got somewhere, although of course what you cite is always a danger.
There's some legitimacy to the substitution approach, because people do e.g. switch from hamburger to chicken when the former gets more expensive (steak, if it was substituted by hamburger, is fraud), and at least this is a special case of production issues vs. something driven by "secular" inflation (drought really wacked cattle production, as my father's friends who raised them attested at the time).
But it's easy to take too far, and any consumer who nonetheless insist on having some steaks, or more expensive hamburger, you'll not be impressed by this statistical substitution trick.
For example, the average household no longer purchases coal or firewood to heat their home, and we no longer buy straw hats. That seems completely reasonable to me. People's preferences change.
On the other hand, we've added radios, TVs, cars, etc. to the basket.
When so much of their spending is automatically tied to them?