Current Limitations

Overpriced Products
There is no denying that Digital card sales are a high-risk industry. The risk component partly explains the high fees imposed by traditional online marketplaces. Those actors impose high commissions on the seller accounting for up to 15% of the final price in addition to fixed fees imposed on routine operations, such as updating the listing price or adding new items.
G2A Table of Fees and Commissions [20]
On the buyer side, some marketplaces will include a service fee, varying from 6% to 13%, depending on the payment method used. The service fee, which also accounts for the problem of overpriced products, is explained by the need for marketplaces to invest heavily in customer support for claim and dispute resolution purposes. Since these marketplaces are the middlemen between buyers and sellers who undergo little to no serious vetting, they need a robust customer support system to intervene if a claim is filed, which costs a lot of money.
Besides, most marketplaces use centralized payment methods which are subject to chargebacks even though the delivery of goods is irrevocable. Payment gateways, thus, rely on higher fees to mitigate the risk of payment reversals.
Service Fee on Eneba
As for the icing on the cake, all these marketplaces impose a payout fee for the sellers—around 1.5% of the amount withdrawn, a fixed fee depending on the payout method, and currency exchange fees. [12]
The result is an inflated retail price by at least 20% and may go as high as 30%.
Grey Marketplace
Most current marketplaces are labeled as “Grey Marketplaces” because users can resell keys bought at a lower price from one region to another at a much higher price. Unfortunately, the reality is much worse. Some sellers are offering hacked or fraudulently obtained keys.
Users have reported that their gaming accounts got blocked after redeeming digital products purchased in those marketplaces [11]. As for the developers, many of them have called to have their games pirated, since they receive little-to-no revenue from sales made on these marketplaces [10].
There is also the risk of ending up with used or invalid products, since anyone can sell on these marketplaces. You will likely get a refund, but it may take a few days, resulting in a loss of time and a bad user experience.
False Positives
Most of these marketplaces rely on centralized payment methods, which negatively affect not only the price of the products, but also the customer experience. These platforms are subject to credit card fraud since most of these digital products are very liquid and easy to resell, without a trace, via Crypto P2P platforms.
To minimize that, most of these marketplaces will implement overly sensitive fraud detection parameters that block legitimate purchases on suspicions of fraud. Moreover, it will trigger unnecessary KYC verifications that will likely make the customer abandon his purchase.