I think even more general lessons are appropriate: "Anyone approaching you trying to sell you something, is selling garbage." which includes ads but also other forms of unsolicited commercial communication. Or "Anyone approaching you, when you can't figure out what it is they want, is likely trying to sell you garbage." You need to have your shields way up these days.
I have never forgotten this since the day I naively sat through a meandering two hour pitch from hell for James Hardie siding.
Honestly, in every area of my life where I have to rely on others, someone has tried to grift me at least once. And that's only the cases where I have definitive evidence.
