I'm pretty sure this isn't true regarding gold. I.e., that some firm has a lot it wants to dump and then spends money convincing people to invest in gold.

Gold is liquid, and the vast majority of it is not held for investment purposes. That is, even if you convinced some people to invest in it, it would not matter much regarding the price.

And consider the costs involved in getting people to actually consider and then act on this recommendation?

But if you have a reference link that refutes this, please provide it.