The following tips will help you to persuade people:

• Ask for something you want when a person is in a good mood. Not very fair but the right technique;
• Smile;
• Emphasize all the benefits of your idea to THEIR further business or life;
• Don’t be afraid to agree with the person but only to some extent. For example, use such phrases as: “Okay, but…” or “Yeah except…”;
• If you really have some false conclusions, admit it – this step will make you look trustworthy;
• Try to analyze why your opponents are against your idea and prepare arguments to overdo them;
• Try your best to sound like a friend and not like a persuader;
• Don’t forget about credibility and authority and if you don’t have them yet use references to reliable sources;
• Know when to give up )))

And always remember the following phrase of Aristotle: … for persuasion to be truly effective, three elements must be present: trust, logic, and emotions.

Use short sentences. Leave empty space between them. Like this.

I often see a very dramatic mistake in my colleague’s letter.
They merge all the text in one paragraph trying to build complicated sentences to make em seem smarter.
Ha ha. Emotions convince. Not Logic.

Nobody will read what seems to provide a head ache at least)
Besides, as it proven, active verbs used in a written way, work and affect like a real boss.

“Do you like our product? Get up and call 555-555-55 right now!”

The thing is, until you say to you potential customer what he should do – he wouldn’t! It is really proved by lot of ad which didn’t contain this addition and that ones which contained! (as a comparison).

One more advice to you letter. USE references!
References from satisfied clients are the most powerful tool of your letter or web site or whatever.
If you don’t have real references – write it by yourself on behalf of friends of acquaintances. Yes, it’s a little trick, but it works and brings the money. As soon as you’ll get references from real clients – you are free to put it with your letter of offer everywhere you wish!