例文は 仕事をさせて頂いた顧客に対するお礼の手紙です。誠意を感じさせる表現と態度 （客先の意見や要望を聞くなど） で失礼の無いよう、お礼を述べることが重要でしょう。

客先を訪問した時などは その内容の如何を問わず、すぐに お礼の手紙を出しておくと良いでしょう。

例文は、簡単な Thank you letter の雛形として使えるものです。特に 難しい表現は ありませんが、 the time and courtesy you extended to　us という表現や the opportunity to speak with you などが英語らしい言葉遣いでしょう。 また、look forward to hearing from you もこんな時の決まり文句です。

Thank you for providing us with the opportunity to be of service to you. It is my sincere hope that you are completely satisfied with our products and services, and will avail yourself of our expertise again in the future.

We are always interested in suggestions that would allow us to improve upon our goods and services, and encourage you to give us your thoughts and comments. Again, thank you.

Dear ＿＿＿＿＿

【謝辞・お礼/サンプル２】

Thank you for the time and courtesy you extended to　us during our visit to your company yesterday. We appreciate having had the opportunity to speak with you　about our products that may be of interest to you.

We look forward to hearing from you and wish to thank you again for your courtesy.