The term for the decks with drill holes or cut corners, perhaps with magic marker along the sides, is that they're canceled. They were used on the casino floor for actual game play and in accordance with whatever gaming authority holds sway, they have to be canceled before they can be released for resale or disposed of. These days, the cards will have been used probably at a blackjack table or maybe baccarat, though the latter isn't as popular in the US as it is in Europe and Asia - poker these days is usually played with plastic decks.
Anyway, after use for anywhere from either a couple of hours to as long as a whole shift (eight hours), they cards are taken from play. In Nevada, prison laborers will sort out the loose cards into complete decks (no jokers or extras) and cancel them - drilling was common up to a decade or so ago, but now sawing off the corner is more popular, box and all, because it's much harder to conceal and keeps cheats from trying to reintroduce the cards to the tables. That's what's in the "dollar-or-less" box at the store.
They're a little broken in, but are actually fairly clean since any casino still using paper cards these days doesn't permit the player to touch the cards - it's too easy to put improvised marks on them - plus many casinos are equipped with autoshufflers, so the cards really don't have a lot of contact with people. Aside from the novelty factor, they're largely considered noncollectable except by those who have a fondness for them. Simply stated, used cards are never as popular as new ones.
The uncanceled decks are the ones that are harder to obtain. When a casino changes the colors or designs on the card backs, the leftover unused cards in the old color/pattern can be "disposed of" without needing to be canceled. As this doesn't happen often, and often when there's little of the old stock left, sealed and uncanceled casino decks are generally a bit scarce and are considered very collectible. Some also have excellent handling properties and shuffle very nicely (most casinos have their decks traditionally cut, which gives them better shuffling characteristics out of the box than other off-the-shelf decks).
Occasionally, there's enough of a design effort put into them that they're pretty attractive as well, but more often than not they're quite generic other than the casino's logo or name branding on the back. Typically they'll have a diamond back pattern (like Bees off the shelf), a "stinger" pattern (same but with fade-to-white edges on the backs and with either bees or four pips in a row in tiny ovals on the corners) or a solid color with a logo.