(NEXSTAR) – Thinking about unloading your old video game collection for some serious loot? Here’s hoping you remembered to keep those cartridges in mint condition.

Top-quality games of yesteryear are currently selling for big bucks at auction, with such titles as “The Legend of Zelda” and “Super Mario 64” going for $870,000 and $1.56 million, respectively, at auctions earlier this year. Other popular games commonly fetch upwards of tens of thousands of dollars, depending of course on their condition and desirability.

“Interest in collectible video games doesn’t seem to be slowing down,” says Valarie McLeckie, the managing director of video games at Texas-based Heritage Auctions.

McLeckie, a collector herself, has been with Heritage Auctions for as long as they’ve been offering games, overseeing the sales of the aforementioned Zelda and Mario titles, among thousands of others.

“People have been collecting video games since video games have been made,” McLeckie notes. “There are people who have been collecting them to build a library of playable games. But there’s also a community that has been actively collecting sealed games since games have been around.”

It’s the gamers in that second group — the ones collecting sealed games — that are more likely to pay up for certain titles. And that’s become especially true in recent years, now that authentication organizations can certify and grade individual copies for collectors.

WataGames, one of the most prominent video-game grading organizations, does this by assigning ratings based on a 10-point scale, taking into account the condition of the cartridges, the manuals and the boxes, and whether the games are still factory-sealed or “complete in box” (CIB), meaning they’ve been opened, but still come with the manual, sleeve, and any other components from the original package. Wata even assigns a grade based on the quality of the shrink wrap on sealed games.

“Their job is whether or not to say whether the game is genuine, or the seal,” says McLeckie, whose auction house utilizes Wata’s ratings when cataloging games.

Certain specific titles, however, are obviously more in-demand than others — sealed or not. But there’s recently been a shift toward more mainstream games, according to McLeckie.

“Prior to this boom in interest in collectible video games, collectors wanted titles that were rare, hard to find. Obscure, even. But with all the recent activity in the market, there’s been an increase in focus on games that have been universally popular, like ‘Super Mario Bros.’”

Games for the Nintendo Entertainment System are among the most coveted, she says, likely because the NES was so universally beloved upon its debut, giving rise to mainstream interest in gaming. But there’s “definitely” interest in games for other consoles, especially original PlayStation titles. In fact, one of the highlights of Heritage’s upcoming video game auction in October is a sealed longbox copy of “Resident Evil” released for PlayStation in 1996.  

“A lot of culturally iconic series got their start on PlayStation,” McLeckie explains.

With buyers having such high standards for certain games produced for specific consoles, it’s no wonder that only the top-tier titles — in near-mint condition — make it to the auction block. But that doesn’t mean everything else is worthless.

The online market for old games in less-than-perfect condition is still strong with collectors. Depending on the title, the right game could fetch hundreds, and sometimes thousands on eBay, according to recent confirmed sales. Just this month, a CIB copy of “Super Mario Bros.” sold for over $240 on eBay, while Wata-graded copies of CIB NES games went for over $1,000. (Loose games, however, were generally selling in the range of tens of dollars.)

“We’re finding that popularity and cultural relevance, combined with high condition in a sealed state, are generally what buyers in the market are hungriest for,” McLeckie says. “But the interesting thing about collectibles is everyone buys into them for different reasons.”

To her point, McLeckie notes that the most valuable games she personally owns are probably a few CIB titles in the Pokemon series, but her absolute favorite game, and the one that holds a special place in her heart, is “Luigi’s Mansion” for the Nintendo GameCube, which she remembers playing — and beating — with her mother when she was younger.

“I’m getting to the point where I’m trying to get really nice CIBs of games that I played as a kid,” she says.

“And finding a sealed copy of a game is hard,” McLeckie says. “That’s not what these games were designed for. They were made to open and play.”