The best way to close a business letter is to strike a careful balance between friendliness and professionalism. The letter should be closed in a way that suggests a more personal touch to the letter but shouldn’t be too formal or informal.
Ideally, you’re looking for a way to close the letter that makes the recipient feel like it’s an authentic message from you, but without feeling too familiar or out-of-place from the rest of the content in the business letter.