Make the letter clear and include only the details that describe the problem and the resolution you want. The sample letter below might help.A business letter is a formal letter. Unlike a résumé or cover letter, it can be more than one page, and is likely to contain six parts. The document discusses the importance of writing thank you letters to customers and provides tips and a template for crafting effective thank you letters. Michigan Free Letter of Intent ( LOI ) Template. Utilize our Letter of Intent to formally express your desire to buy a product or service. Sample Letter 7.30 thanks a customer for continued business support. Sample Letter 7.31 thanks a customer for repeat business. How to write business letters to convince your recipient to respond or act.