This part is definitely true. 4chan users will block your advertisements and can smell shilling and astroturfing from a mile away.
"Unwilling to pay for things" I'm not sure is 100% accurate. 4chan may be home to pirates, cheapskates, and free software advocates, but it's also home to some of the most dedicated hobbyists, collectors, and consumers in the world. See /g/'s "battlestation" threads (incredibly decked-out computer rooms), the girls of the cosplay board who spend hundreds or even thousands of dollars on costumes and obscure fashion, the people who travel to Japan twice a year to buy pornographic comic books at Comiket, and so on.
I think there are opportunities to be found here, but you have to be an active member of some board to know what its needs are, and even then it would involve a lot more elbow grease than achieving success among a less savvy userbase might. Just making an app and buying some ads isn't going to get you anywhere. There is precedent here, however, in indie game development, where it's fairly common at this point for new devs to be 4chan users who get most of their early attention and users from threads on /v/ or the amateur game development generals.
EDIT: Some random ideas for small businesses or small startups that could be marketed to 4chan effectively:
Retro console repair and modding services would be popular on the retro games board.
The fan translation scenes for anime, manga, and video games are mostly controlled by 4chan users at this point. Many of these groups could go legit with some funding (see Crunchyroll, which was basically an anime fansubbing group that got the funding to acquire broadcast rights for simulcasted subtitled anime and grew very quickly, or Carpe Fulgur, two goons that translate Japanese indie games).
Import services are an obvious choice. Indeed, jlist has been advertising with 4chan almost since its inception, and there's no reason there couldn't be more competition in this space.