Moderators: Moderator Team, Admin Team
markystar wrote:hmmmmm
good question.
the obvious answer, which you already know, is ありがとうございます is non-past and ありがとうございました is past. in many situations the 2 are interchangeable.
ありがとうございました has a bit of a sense of finality to it, as in the action/service or conversation is finished. for example, at a restaurant when you leave they will say ありがとうございました because you are leaving and then transaction is complete.
i don't know if that helps or just confuses the issue. if you use ありがとうございます instead of ありがとうございました it wouldn't be wrong because you're covered by the present and future tense possibilities of the word. but if you misuse ありがとうございました you only run the risk of sounding unnatural but wouldn't be rude or anything.