I can’t see how this is true as there are tons of companies selling access to data obtained from the Twitter API such as social media monitoring companies (Sprinklr, Meltwater)
If you are creating a Twitter app, and letting users login via Twitter and then using those user tokens to make API calls, that’s a good first step, I am not sure if you are doing this already.
Other than that, I would just make sure you position your service as something that benefits Twitter, describe it as something that allows you to create better tweets or engage with your followers better. The internet is filled with apps that sell Twitter data like Mention.com, SocialRank, and Social Animal.
As a counterpoint, stock data is freely available (through online websites, your broker/app, etc), yet it costs thousands of dollars per month to actually license and acquire such data through the proper channels. Trying to build a business based on scraping such data (or even using your broker's free personal-use API) will get you in trouble pretty quick by the exchanges.
That's true in a sense. But I would still be paying them money to receive data from Twitter. So in a sense, yes, I am paying for Twitter data. In any case, I have a hard time seeing how this wouldn't violate the ToS.