Hmmm. My personal take, going by your perspective (if it's true the retailer only has the ONE figure, and it's opened): My view, if it's opened, there is NO WAY they should be charging someone full price for something that's been opened. But I am not a scalper, a "I buy to sell later" type of person. I don't hoard boxes of unopened product just to make a profit. I can generally only afford ONE of each figure, and I open EVERYTHING. I don't even keep the boxes that these things come in (frankly it just takes up too much space). IF the retailer has additional stock of the item being displayed, then I don't see a problem with them charging full retail (or whatever their discounted retail price might be -- assuming they offer one). Steve at Timewalker has a number of figures on display, but it's my understanding that those that are are part of his own personal collection, and therefore not for sale (it's just a way, as shazzdan put it, to generate sales).
I guess it depends on the school of thought of your retailer, Roger. If he believes something is just as valuable, due to "rarity", as something that hasn't been opened, and if someone is willing to pay that price...
I don't have a choice but order online myself, as the closest brick and mortar that I can go to is Timewalker (which I do a lot of business with), and they're 8.5 hours away (not something I'm willing to do, when they ship stuff to me for free in about 2 days). Sad thing is Big Bad Toy Store (which is only a warehouse) is 22 miles from my house (but you can't GO there, shipping isn't free -- and it takes about 10 days).
Online purchasing, of course, as we all know, is a crap-shoot. It sucks that this hobby is set up so strangely. It's nice to be able to wait until you can actually SEE the product 1st hand, but then you run the risk of the retailer not being able to get more, or it being sold out online. Steve at TW has told me that when it comes to HT figures, Sideshow can be a real pain in the ass to work with. Once the original PO numbers have gone off to SS (the distributor) and he receives the allotment he ordered, if he sells out on PO, SS RARELY lets them have more stock to fulfill customer demand (probably because SS is run by a bunch of greedy a-holes who ALWAYS charge full price for new items and they make additional profit on their outrageous "shipping and handling").
You're kind of stuck between a rock and a hard place. If you never buy until you see the product in hand, as I said, you run the risk of not being able to find it online, or paying full price for a displayed item (if you really want it that bad). OR you PO, like I do, and run the risk of getting a crap product (ThreeZero's Major Motoko, Asmus' Selene).