Thank you for allowing me to assist you. The following is the information that you requested. I provide a complete sample letter, all you need to do is fill in the personal information, (such as name, address,etc,) that you did not provide for me. In addition, I provide a custom example, but since you did not elaborate on what type of client of non-profit, or what you did for them, all you need to do is insert where it says "specific".
The entire letter should be in 14 FONT.
(Your CIty, State, Zip Code)
Dear Madam/ Sir,
(Your Name) is an intelligent and business minded individual. He/She is a previous client for our organization. This as afforded me the opportunity to observe (Your First Name) working and interacting with several members of our organization. He/She has always proven to be a dependable, and trustworthy worker that has always fulfilled all deadlines on time and with the quality to detail.
The following is the capacity that (your name) has provided our organization with services; (list what you do for a client).
In addition to fulfilling all obligations, (your name) has a unique business aptitude that has been quite helpful with our business. He/She is very successful with all business communication strategies and projects. The current business communication project that (your name) is working on represents the quality that one would expect from a veteran employee. This is an individual worthy of consideration.
It was a pleasure doing this for you today. Please remember to click the accept button, and feel free to request me anytime.
Have a great day