I didn't say that. You could be kicked from default trust for saying "hello" too much. Its completely up to whoever trusted you in the first place. As you have said, there is no rule saying you can't sell trust, there is also no rule saying you can't give inaccurate feedback. There are no rules to the trust system at all, the community makes up the guidelines, and selling trust is generally frowned upon. The chances of you being removed from default trust by whoever added you in the first place when they find out you are selling trust is incredibly high. And if they don't, whoever added that person to default trust may re evaluate based on that person's inaction.

That said, I do believe this is all a hypothetical situation, because anyone actually on default trust understands how it works better than what you are displaying. Not to say that this hypothetical question isn't worth addressing.