How Cardmarket Blocks Fake Accounts and Bot Attacks at Scale with SEON

About Cardmarket

Cardmarket is Europe’s largest online marketplace for collectible card games, including Magic: The Gathering, Yu-Gi-Oh! and Pokémon. With over 150 million listings and tens of thousands of active users, the platform enables secure, cross-border transactions between buyers and sellers across Europe.

Challenge

As Cardmarket scaled, the platform became a target for fraud rings and bot attacks, especially during high-demand periods. Fraudsters created waves of fake accounts that triggered internal alerts, skewed marketing metrics and drained fraud and support resources.

Key challenges included:

• Coordinated bot attacks: Systematic fake account waves using randomized emails and proxies to bypass basic defenses
• Resource drain: Manual review of suspicious accounts consumed fraud and customer service team bandwidth
• Data contamination: Fake registrations distorted sign-up data and disrupted attribution tracking for marketing

“We wanted a way to proactively stop fake sign-ups without adding friction for real users.”

Olivier Novel, Fraud Analyst, Cardmarket

Solution

Cardmarket chose SEON to block fake accounts and bots at the source: registration. With real-time signals, flexible no-code rules and hands-on fraud expertise, SEON became a strategic partner across the risk and growth teams.

Why SEON:

• Automated bot detection at scale: SEON identified and flagged suspicious registrations during bot surges, freeing up team resources and preventing downstream risk.
• Intelligent rule-building: Cardmarket built custom rules targeting known patterns, such as sign-ups from the same IP with randomized email formats, stopping attacks without hurting UX.
• Fraud expert support: SEON specialists helped the team refine detection rules, analyze trends and adapt quickly to new attack methods.
• Digital footprint insights: SEON’s signals helped uncover how attackers targeted specific landing pages, providing visibility to the marketing team and supporting funnel security improvements.

Results

Since implementation, SEON has significantly improved operational efficiency and risk detection across the platform.

Highlights:

• Eliminated bot swarms at onboarding
  Dozens of fake accounts per attack wave are now blocked in real time, before they impact the platform or data integrity.
• Screened 2,000+ registrations daily
  Every new account is evaluated without impacting performance or legitimate user experience.
• Freed up customer support
  By automating fake account detection, SEON reduced manual workload, allowing teams to focus on high-value tasks.
• Improved marketing visibility
  SEON revealed which localized landing pages were being exploited, enabling proactive funnel adjustments.

Conclusion

SEON helped Cardmarket turn a vulnerability into an advantage. The platform now screens thousands of sign-ups in real time, blocks malicious actors before they get in and surfaces risk insights that benefit fraud, support and marketing teams. With no engineering lift required and no customer friction added, Cardmarket’s defense is now as seamless as its user experience.