I found Rita McGrath note on lost customers very instructive. Please note particularly:
“From my vantage point [on a Café Nero in a train station] just opposite the entrance, I was able to observe customers coming and going. I was fascinated to see how many of them came and went — without buying anything — because they took one look at how long the line was and abandoned their coffee mission then and there. Intrigued, I started to count. Fully 3 people looked at the line and bailed on the thought of purchasing for every 1 person who actually made a purchase. Imagine — the café would have increased its business by 300% if everybody who thought they might like a coffee had been converted into a coffee buyer. And this is at a train station, where people risk missing a train if they stand around!”
How Many Customers Did You Lose Today?