Try telling that to the SEC who deals with thousands of non-disclosed compensated issues each year. ANY form of compensation for ANY services provided to a publicly traded company are supposed to be legally disclosed WHEN/IF the person receiving that form of compensation chooses to promote said public company in a public message board forum format.
And the reason the SEC requires that disclosure is so that any readers of those compensated posters views/opinions get the entire picture b4 relying on their views expressed.