Proper closing closing to a letter of appreciation?

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

Yours Sincerely

Sincerely yours, Very truly yours or Sincerely.

The proper way to use this would be:Your friend,: )

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