Imagine you’re walking down the street and you see something in a store window that catches your eye. You walk to the front door and there’s a sign that says, "No Browsing. Serious shoppers only." Or maybe there’s a bouncer and he asks to see a credit card or some cash to make sure you’re a legitimate customer, and not just killing time, or worse, plan on shoplifting.
How welcoming would that be? Even at stores that market their exclusivity, I imagine this would be a big turnoff for most people. I suspect few retail shops require this type of proof-of-(future)-purchase.
Yet, businesses have no problem treating online prospects with the "guilty until proven innocent" mentality. Case in point:

I can understand (kind of) why people use something like this for personal emails. You figure that if your long lost buddy from college is trying to get in touch with you he’ll click that link. However, is this the welcome you want to offer prospects?
Remember, most successful retail shops hire greeters, not bouncers.



