The revenue share, and what it actually costs
The default in this industry is a percentage of gross gaming revenue, for as long as you use the platform. It is easy to accept because it starts small and asks for nothing up front. The part worth working out before you sign is that it never ends and it scales with your success: the better you trade, the more you pay, and a book that grows for five years pays many times what the platform cost to build. It is a good deal for an operator who might not last a year, and a poor one for an operator who does.