Ultimately, it's going to vary on many more factors than the casino, but I think I can sort of answer the question
does this lack of reuse factor into the build quality of the cards?
First I should note that as I started Googling around for an answer to this, it is abundantly clear that there is not a definitive answer on this. This answer will assume you're talking about plastic playing cards since paper playing cards have such a short life span that they probably couldn't be resold.
There also is a lot of discrepancy on the length of time a casino even uses a pack of cards before retiring them. I have seen references that the Bellagio uses a deck of plastic playing cards for poker for 2 months, but this isn't official or even supported. That same page has a user saying they saw on a TV show that cards are used between 2 and 24 hours depending on what game it is and how they are shuffled, a claim that is impossible to check. This probably refers more to games like blackjack, where the house's money is on the line and they'd want to ensure that no money would be lost because players could identify cards.
The best information I could even find relating to casino cards was on the COPAG Cards website. In talking about use of their cards in casinos, they say
The primary use for 100% plastic playing cards in the casino is in the poker room. Since poker is a game where the players handle the cards extensively, plastic cards are preferred due to the durability and additional security that they provide over their paper counterparts. COPAG cards are used in casinos throughout the world and are dealt in many of the finest poker rooms across the United States.
Later in that same FAQ, there is this question and answer:
How long will COPAG cards last?
The longevity of your COPAG cards differs depending on how they are handled during play. Therefore, we can not give an accurate length of time that they will last. However, 100% plastic playing cards will last significantly longer than paper playing cards.
This is where I'm going to do some fuzzy logic. Given that on the same website they a.) talk about their cards being used for poker in casinos, and b.) they talk about the length their cards will last as if answering anyone that could buy their cards (and you can buy COPAG cards from their website), I would think that the used cards you buy from a casino are not qualitatively different than the cards you could buy new from a store, except that they've already been used.
I'm unsure how long a pack of plastic cards normally lasts since this also varies on how much it's used and how rough it's shuffled and myriad other factors. If you knew that, you could guess that any used pack you buy from a casino will have either 1.) months of almost constant play reduced from their life if they were used for poker, or 2.) a much smaller amount of time, potentially only a few hours of play, reduced from their life if they were used in games where the house's money was at stake.
Edit:
Figures that just after I post this, I noticed that there are separate tabs for purchasing on the COPAG website for retail and casinos, so some clarification is needed. On the retail purchasing tab, the plastic poker cards are measured at 63mm by 88mm. On the casino tab, the size of plastic poker cards is 63mm by 88mm. They are the same size.
Additionally, I would think there is no qualitative difference between the two for economic reasons. It wouldn't be cost efficient to have separate machines for different qualities of plastic for different cards, but changing the pattern on the back would be pretty simple.
A casino couldn’t survive without millions of decks of cards. They are manufactured to a higher standard than regular decks and they produce some fascinating facts. Here are some of your common questions answered.
How Long Does a Casino Use a Deck of Cards?
How many times are casino cards used in their lifetime? If a pack is used in a single deck game, they may last up to eight to twelve hours. If they are in a multi hand game, it may be a little longer. There is a high turnover of hands and decks will not have a long shelf life.
How Many Decks of Cards Do Casinos Use in a Day?
The answer depends on whether there are imperfections or if cards are damaged in any way during their use. What we do know is that the United States Playing Card Company, the biggest of all card producers, sells over 20 million decks to casinos every year.
Why Are There Holes in Casino Cards?
When a deck of cards is no longer fit for use or it is to be taken out of service, holes will be punched in each card. This effectively cancels the deck and ensures that it cannot be used later on. It’s a simple system that casinos employ to prevent cheating.
Why Do Casino Cards Have Cut Corners?
Trimming cards – cutting the corners off – has the same effect as punching holes. This cancels the deck and ensures that they cannot reappear at the casino in the future. Trimming will take place when the cards reach their time limit or have become damaged in any way.
What Do Casinos do with Old Cards?
This depends on the casino: Some will destroy them while others will donate decks or sell them in their gift shops. Cards from some casinos in Nevada will send them to a local prison where the inmates will cancel them and potentially use them for games.
Where Can I Buy Used Casino Cards?
Check in the casino gift shop and ask at the desk: Alternatively, if you cannot find a deck onsite or you are not travelling to a casino, it may be possible to buy cards online. Have a look on eBay or other websites that sell or auction collectable items.
How Much Do Used Casino Cards Cost?
Used casino cards are not very expensive to buy. They are collectable but not easy to use in a game so you may be able to pay between a few cents to prices in the region of $8 USD. Unopened decks are more expensive and if these would cost a few dollars more.
Since When Did Casinos Cancel Cards?
It’s unclear as to when this practise began. We are aware that casino poker chips have been replaced regularly since the 1980s so this could be a clue. However, cards wear out more quickly than plastic chips so card cancelling may have started much earlier.
What Are The Techniques for Marking Used Casino Cards?
There are many techniques that can be used: Punch holes and trimming cancel cards while casinos will use other processes. A black ink marker is common in Nevada while other states and locations around the world may employ shading, tinting or some other form of cutting out.
What Is A Riffle Test?
A riffle test is a process used to determine if cards are marked. An experienced member of the team will riffle through and any marked cards will stand out because they will either move around or any markings will make them stand out through reflected light.
Closing Thoughts
All of these techniques are there to ensure fair play. Anyone looking to play at a casino should be reassured that cards are changed regularly while processes are in place to uncover marked decks.