Proper closing closing to a thank you letter?

If it is to an acquantance and started with Dear John for example then you can finish with yours sincerely. If to a business and started Dear Sirs then finish yours faithfully

How Can i write letter of appreciation?

Yours Sincerely

Sincerely yours, Very truly yours or Sincerely.

Thanks so much for being the nice, caring person I've always known you are!