You will find that it is in your best interest to have them link to your site not theirs! If you had spent a lot of time and effort to get your site ranking well would you give a nobody with a nothing site a free ride? That is what I found to be the problem, what can you give them that they need? as they don't need you? that is where the challenge is, work that bit out before you waste your emails.
Hope this is some help.