Platform Fee is a key term in the world of online marketplaces. It is a revenue model utilized by platforms to generate income. A Platform Fee is a charge that a marketplace platform imposes on its users for the faciliting services it provides. These services include connecting sellers with buyers, providing necessary infrastructure for transactions, and ensuring a secure and smooth transaction process.

The formula for the Platform Fee may differ from one platform to another, but it generally consists of a percentage of the transaction amount (commission) or a fixed cost. Sometimes it could be a combination of both. For instance, a platform might charge a 10% commission on the transaction amount as well as a fixed fee of $1 per transaction.

With the commission model, if a seller successfully sells a product for $100, the marketplace would take $10 (10% of $100) as their fee. On the other hand, the fixed cost model implies that the same fee is charged regardless of the transaction value. So, whether a product is sold for $100 or $1000, the platform would collect a fixed fee such as $1.  

In the hybrid commission and fixed fee model, the platform would charge a 10% commission and a $1 fixed fee. So, if a seller sells a product for $100, the platform would take $11 in total as their fee ($10 as 10% of the transaction amount and $1 as the fixed fee).

Examples of platforms that use these fee models are abundant. Amazon, for example, charges a referral fee (commission-based) that can range from 6% to 45% depending on the product category. eBay, another example, uses a combination of fixed and commission-based fees, charging an insertion fee (fixed fee) and a final value fee (commission).

These Platform Fees represent the price sellers pay to gain access to the customer base and dependencies facilitated by the marketplace platform. In return for payment of the Platform Fee, the marketplace will handle customer acquisition, payment processing, possible customer service, and other operational aspects that sellers would otherwise have to manage on their own.

Platform Fees are crucial in sustaining the business model of marketplace platforms as they usually represent their primary revenue stream. By keeping these fees reasonable and transparent, platforms can attract and retain users, thereby enlarging their market share and sustaining their business in the long run.