The language used in the sales letter format should be simple, and suited to your trade. Complicated or complex writing leaves the reader confused and unlikely to read your letter or take action and buy. When a letter writer includes any bonuses, they should be supported with the word "free." For example: "FREE article submission with every SEO article!"
Overall, having the correct letter format will guarantee people that they can have the upper edge against other job applicants. All they need to do is to keep it clean and unique. There is no need to have a very extravagant cover letter. Just indicate all the essential things needed that can help them to get the job they need.