In this case, you would not want a letter. You will need to draft an Independent Contractor Agreement
---a contract---which sets out the duties to be performed, the compensation and requires that they have business licenses
in the state or city that they work out of.
You will not be allowed to dictate the hours that they work, nor set the order of appointments they have if this a lead generated business. You will need to clearly state that neither party has the obligation, nor will they, collect or pay federal or state taxes on behalf of the other. Also it is generally demanded that they carry business insurance and auto insurance as well---as independent or not--there can be an argument made that they are your agent---and at least bring you into a suit as a defendant.
This is a contract that will need to be drafted by an attorney---unless you like living dangerously. If you do, then you may modify this document for your use:
I wish you the best in 2011.
Because I help people here, like you, for a living---this is not a hobby for me, and I sincerely XXXXX XXXXX abiding by the honor system as regards XXXXX XXXXX I wish you and your family the best in your respective futures.
Would you be so kind as to Accept my Answer so that I may be compensated for assisting you? Bonuses for greatly informative and helpful answers are very much appreciated. Thanks Again,