I think the most effective action you can take is to to ACKNOWLEDGE your customer ASAP. Even if you are involved with another customer or on the phone, a simple wave of your hand or a nod will suffice to acknowledge your customer. Everyone wants respect, wants to feel he (she) matters. No one enjoys being ignored.
If I were your salesman and saw a potential buyer outside kicking tires, I'd go out, introduce myself, and ask if I could help you. If you are just browsing, it makes it easy for the customer to refuse further interaction. If you really have a question or want a price, better yet. Then I'd say, "if you need more help, come in and ask for (Larry), I'll be around the showroom, or in the second office to the right, (or wherever). Or just ask the first person you see."
Every person in the building would be coached (required!) to make eye contact, greet the customer, even the parts man, the janitor or the bookkeeper and/or the OWNER.
I drive right past my small town auto parts store multiple times per month these days. I used to spend some money there, and they all knew me by name. One day I walked in and the owner was out front discussing politics or weather with a guy. I had to walk right between them. Not a sign that I was there. The owners son came scurrying up from the back, looked me right in the eye, made a hard left and picked up the phone laying on the counter. Not a sign I was even alive. Only the part time high school kid had the sense to say "Hi Larry, we are backed up a bit, be with you in a second", then went back to the guy in front of his counter.
My wife was a receptionist in a medical office. She said EVERYONE got a Hello, a Thanks for coming (or, for your business) and a Goodbye, at minimum.