I work at OpenAI and I can assure you that if we say we don't train on your data, we don't.
I acknowledge that if you don't trust OpenAI, then you may not trust me either. But lying about this would be bad for legal liability, customer retention, and employee retention. Even if you model us as evil (and we really aren't), it's still not obvious to me that it would be a good decision to lie. As soon as a whistleblower revealed the scam, it would tank revenue and employee morale.