Is my business liable even if I just use standard ChatGPT and have not built a custom bot?

Yes. Liability attaches to use, not to custom development. As soon as you use the bot in a business context — whether as a customer-support tool, sales assistant, or internal helper with customer contact — you are the controller under DSGVO and a commercial actor under UWG. The provider (OpenAI, Anthropic, Microsoft) is merely a data processor. Responsibility towards your customers rests entirely with you, and the OLG Hamm cemented exactly that point in the Aesthetify ruling.