Retail employees knowing about panel lottery:
Yeah, that would be quite rare. They might have heard of a few more popular models, but they can't possibly keep track of every model. But if he's saying there's not much difference between the panel alternatives, and it's mostly processing and room temperature (...?), then he's gravely mistaken or deliberately lying to you, maybe trying to lull you into buying the product. But most probably he's just not that educated in the matter. You can check this by asking whether he can tell you about pros and cons of, say, VA vs IPS. If he starts to focus on something else like "LED panels", then you know he probably has no idea what you're talking about.
Though you can't blame him, it IS an enthusiast matter, wouldn't expect them to know very much about it.
As for restocking, etc:
Well, unless the panel type is clearly advertised within the product details, then it wouldn't be considered as a faulty one.
Here are two threads discussing the re-stocking fee and its legality:
http://www.ukbusinessforums.co.uk/threads/restocking-fee.51206/
http://www.theregister.co.uk/2010/04/16/online_refunds/
In summary: EU has built quite a strong defense for the consumer, and the retailer is usually the one who gets stuck with the bills.
But again, this is a fairly special case. From what I've understood, the DSR basically gives the buyer an opportunity to "inspect" the merchandise like he could in a store, before making a buying decision. But if it's only a sealed package on the store, then it wouldn't help you much, in any case. If it was on display on the store, you could easily check the label on the store, so you should have the same opportunity if you order it online, right? Unfortunately, I don't think the DSR makes a distinction on these sort of cases. The stores have no obligation to have sample units on display, so you might have a hard time convincing them of your right to have it opened. Though not entirely impossible, mind you.
For comparison:
In Finland, there are few brick-and-mortar stores (with online fronts as well), which offer a free service that guarantees 30 days of return, no questions asked. While they will surely take a small hit because of people taking advantage of this, they also gather a lot of consumer trust because of it. This is a fairly competent business tactic.
Personally, I would vote with my wallet, and support the stores that do offer this kind of extra service. Simply put, if you don't find one retailer's terms&conditions acceptable, then go to the next store. Competition will eventually take care of the bottom feeders.
Though it is indeed unfair for the seller if the customer simply "changes his mind" after opening the product, after which the seller is left paying for the customer's mistake.
Hmm, maybe you could suggest that they try to contact the supplier to inquire the panel type, perhaps they might know? Alternatively, you could contact Samsung directly and ask whether there's a way to easily differentiate between different patches.
If all this fails, then maybe it's better to just purchase a computer monitor.