The answer is simple, study and communication. Any time you want to learn a new subject your best courses of action are to read about it and then get involved in it. First familiarize your employees with the product, have them read online reviews and forums. Have them read the source material and magazines. After they have familiarized themselves with the product in question, usually one or two of them will be interested enough to try it out. Encourage them by giving them a small amount of free product to build, paint, and understand the tactile feel of the hobby. After they have finished building and painting their models they now have an idea about what their customer will be experiencing when the first get their product, while also teaching them important facts about each product itself. Once the employees have a grasp of the product, begin training them on basic customer communication.
In the service industry, which is what retail, arguably, is, the customer is always right. Unless they are horribly wrong. This is what I refer to as "Haves, Wants, and Needs." These are the three basic bits of information an employee should ascertain from the customer before the employee sells them any product. This is done through engaging and communicating with each customer who enters the store and browses the wargaming section.
BUT WAIT, you scream at the top of your lungs, THIS SOUNDS LIKE A GW TACTIC!
You would be correct. There is a reason their B&M stores used to function really well. They had staff who knew the product, could ascertain what the customer wanted, and sell the customer what they needed. The only issue arose when the management of the stores pushed their "red shirts" to turn profits instead of create loyalty. This is something 3rd party B&Ms have in their favor. They don't have a regional manager looking at the bottom line who has no interaction with the customers on a daily or even weekly basis.
WHAT IF I AM JUST BROWSING, you loudly shout, I DON'T ALWAYS WANT TO BUY SOMETHING!
Then bloody say so. You are walking into a retail store. You are then assumed to be there to purchase an item. The employees of the retail locations should assume you are there to purchase an item. They should approach you and initiate communication. If you wish to not be helped, tell them so nicely. Respect goes both ways. Don't be a cunt.