Just the best - simple

We will be giving very positive views on White as a property agent to friends in the area as we have had excellent service from you which I’m sure will continue throughout the tenancy

Thank you, (we) couldn't have asked for nicer agents to be working with on this!.

I just wanted to say thank you for all your help and hard work throughout my very long sale and purchase.

I want to say a very sincere thank you for all your hard work on my behalf, you are a gem. I hope Mr White knows how lucky he is to have you!