I understand that both expressions are acceptable translations of “no, thank you” in order to politely answer no to a question.
Are they always interchangeable? In which situations would we use one over the other?
Likewise I’m interested if “спасибо да” and “да спасибо” can be used to politely answer yes to a question. And if so, when would we use one or the other?
Спасибо, нет typically shows that the speaker is actually not too grateful for the suggestion. The version Нет, спасибо sounds (depending on intonation) as a neutral to polite refusal (like, I'm grateful to you but have to refuse, I don't want it).
Спасибо, да (unlike Да, спасибо) is rarely used (and just colloquially - it doesn't sound sophisticated enough, despite the sense is the same).
That depends on the intonation.
спасибо, нет pronounced without special tonal modulations sounds more assertive and categorical and by extension less polite. нет here usually receives intonational stress, in part because of its placement at the end which is a usual location for words requiring special emphasis.
To make it sound polite a greater effort needs to be invested into the intonation.
Same goes for спасибо, да which sounds curter and therefore a bit less courteous.
But since generally politeness is required for conveying unpleasant information such as refusal, the difference between the phrases with нет is more significant.
