Dear …
I want to take this opportunity to say how impressed I was with the professionalism __(name)__ demonstrated as __(he/she)__ helped me to __(obtain the appropriate building permit/documents/etc.)__ for __(building my garage/house/my case/etc.)__. I found that__(he/she)__ was exceptionally helpful, willing to assist me in any way __(he/she)__could.
__(Name’s)__ dedication and efforts are nothing short of exceptional. __(He/She)__ took the time to review and completely understand my __(project/case/situation/etc.)__. __(He/She)__ was both thorough and efficient, which gave me full confidence in the suggestions __(he/she)__ made. In addition, __(he/she)__ proved to be an excellent liaison between __(name the parties involved)__ and did whatever __(he/she)__ could to expedite the process.
I must commend __(name)__ on __(his/her)__ outstanding efforts. __(He/She)__ is an excellent representative of __(name of organization)__ and is a pleasure, indeed, to deal with.
Sincerely,