Dear {Recipient},

I would like to extend my gratitude for the {type of} services you provided gratis recently. In addition to your generous gesture, I truly appreciate the level of detail and accountability you demonstrated, as you do on each {project/transaction/etc.}.

I have and will continue to recommend your services to other {companies/individuals} in need of {type of service provided}. I look forward to working with you for years to come!

Sincerely,
{Your Name}

Dear {Recipient},

Thanks so much for visiting me while you were in town. It's been a while since we've since each other, so I'm really glad I had a chance to catch up with you.

{Recall something worth mentioning from your conversation or meeting.}

Please stay in touch. I hope I can visit you in {recipient's city/town} soon!

Warmly,
{Your Name}