We recently came across a 1yr old female Shih Tzu which we really like, the only problem is it sleeps on the owners bed, if we bought it we would want it to sleep downstairs in the kitchen, how do we do this without letting the dog sleep in our bed for the first few nights?

Being rehomed will be strange and disturbing to any dog. I would crate it. Buy it a small crate to be its den and find a corner in the kitchen for it. Read the sticky starting at https://www.askmehelpdesk.com/dogs/i...tml#post251802
It is meant for young puppies, but a good introduction for any new dog owner.

Take her seriously, giving her good leadership from the start. Sleeping in the owners' bed may have given her the wrong idea about her status. It may even mean riding home in the crate. The key to most behavior problems is approaching things using the dog's natural instincts. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at Raising Your Dog with the Monks of New Skete For more on being top dog, see Establishing and Keeping Alpha Position, Letting your dog know you are the boss

As labman say you could try crating her you may also ask current owner for old garment with their scent on it to make the transition a little less traumatic for her be prepared for a few sleepless nights as you would with a new puppy and then just enjoy your new pet

I haven't had a sleepless night with a new puppy for the last dozen or more. See https://www.askmehelpdesk.com/dogs/i...tml#post251802