Following a decades-long downturn due to overproduction and dwindling interest, the trading card industry is booming.

The state of play: The boom was aided by the emergence of grading agencies, which fundamentally changed the art of card collecting, while attracting a new type of clientele and, in some cases, incentivizing fraud.

The backdrop: Modern baseball card collecting erupted in the 1990s, when agencies began grading cards on a 1–10 scale, making their value more standardized.

• This gave hobbyists a sense of a card's market value and provided an easy way upgrade their collections: simply purchase a higher-graded card.
• But it also attracted a new type of collector — one who viewed trading cards as a financial asset, similar to stocks or works of fine art.
• It also led to an increase in "card trimming" — the process of altering cards to increase their value. This can include using bleach to remove blemishes or scissors to make edges look cleaner.

How grading works: Collectors pay to send a card to a grading agency, which evaluates it and provides a grade. This is helpful for potential buyers and sellers, but it also attracts fraudulent actors.

• There's little transparency about the way grades are determined, or how graders are trained, creating a system ripe for corruption.
• Collectors have raised concerns about "cozy relationships between certain submitters and grading agencies resulting in high grades that seem to be a statistical anomaly," writes The Athletic's Katie Strang (subscription).
• Last July, the FBI launched an investigation into a well-known collector, a top grading agency and a major auction house. The case is ongoing, but its impact has already been felt, eroding trust in an industry that's built on it.

The big picture: The internet helped ignite the trading card boom, but it also opened the door to people looking to enrich themselves by exploiting the system. They do their damage from a distance — a far cry from the early days of card collecting, when there was a greater sense of community.

• The market for top cards on eBay is inflated due to an unethical practice called "card rigging," writes The Action Network's Darren Rovell.
• How it works: A group of sellers buys up the best version of a certain card (i.e. a rookie card with a 9.5 grade). They then buy the card's lower-graded versions and shill-bid (bid on their own item) to drive up the price.
• The public then thinks the card went for that value (even if they won it themselves and never paid for it). And with that price serving as a reference, "the higher-graded top exemplar makes a huge profit," writes Rovell.

The bottom line: Trading cards are booming, but so is industry fraud. And while nostalgia and a love for sports are still part of the experience, card collecting — and the card-collecting community — have evolved.