Grazie is the shortened form of ringrazio and thus they are interchangeable. In practical terms ringrazio is ever so slightly more formal and is often used by clerks, cab drivers etc., people who are performing a service. On the other hand, as is the case here I believe, it is used when you are particularly thankful to the other person/people. I say that because a person providing a service would never use ti when speaking to a customer.
I have got to the stage where on first seeing something new I try to stay close to the Italian. Grateful that 'I thank you a lot' accepted but not a sentence a native speaker would say. Pleased to see 'Thank you very much' is given as answer. I am native English (UK) speaker.