@WBYeats,
There seems to be some meme among Asians that best wishes is a common complimentary close in English business practice. Speaking for American business practice, i have never seen it used. The rule i long followed (i was a business manager for many, many years, which often involved being my own secretary) "Sincerely your" when addressing someone known to the author, "Yours truly" (or a variation thereof) when the addressee was not known to the author, and "Cordially" when one did not feel at all cordial, and want to close the letter as coldly as possible. These things i learned in the 1960s, which was a long time ago, but change in the formalities in business practice takes place at a glacial pace.