Why care?
If you wish to sell sunglasses, then it could be as easy as buying Sunglass Racks and letting people decide, but while you're at it you, should make the job even easier to the client. How can it be easier than looking and walking? That is actually the key; you should try to cut down on the amount of looking and walking the customer does.

Where should the sunglass displays go?
Depending on how you actually want to tackle the market, there are two different ways to deal with this issue.

If you place your sunglass racks facing the entry point of your store, then you hope that the customer was searching for sunglasses to begin with. Customers are more conscious of what they buy when entering a store than when they are leaving, with that mind, if you decide to go with this approach, you will attract customers that came to your store for sunglasses (among other things.) I would recommend this method if the prices of your sunglasses are higher than normal, as you will not attract as many impulsive buyers as the second approach.

The second key position is to place your sunglass display near the cash register. This method allows the customers to browse through your sunglasses while they wait in line; however, this tactic relies heavily on the fact that the customer is an impulsive buyer (he or she was not even thinking about buying a pair of sunglasses in the first place). With this method, you are less likely to sell an expensive pair of sunglass, but you will likely sell more pairs that the average customer will categorize as inexpensive.

What Kind of Sunglass Displays?
This is another issue that seems simple (and actually is) but which shouldn't be neglected. Roaming through stores, we have all seen sunglass racks that are shaped like columns, and with an easy push, will rotate graciously for the consumer. This may sound simplistic, but this technique is quite beneficial. By allowing the rack to rotate, you allow the customer to quickly view different selections without actually asking them to move around. Since your customer is going to try on sunglasses, you might as well allow them to be motionless.

If you positioned your sunglasses near the cash register, then you may want to look at a different approach. In this scenario, we cannot stop the customer from moving, since he or she is most likely standing in line. For this application a waist-level small and very long rack will grab the attention of the customer throughout the time that they wait in line.

For Your Eyes
You should also use the subliminal technique used in grocery stores of showing off your best pairs of sunglasses (whether it be the most expensive one or the cheapest is up to you) on a rack that is at the same level as the customer's eyes. This way, you will be sure that this particular item is the first one seen when the person walks into the store.