What is quite etiquette

[BG2015]

Had some quotes for a landscaping project and have chosen who we want.

What do we say to the others?

Thank you but we have chosen another design/direction/option.

As @Pipandmum suggests, but frankly anything as long as you tell them.
I didn't mind not getting business after doing a quote for someone, but I hated not knowing, especially when they seemed keen and you are not sure whether to keep a space in your diary for them.