Whoever handles the credit card fees is going to need to cover his costs, which depending on the credit card used will usually be in the range of 3-4% of the total charged, plus 30-50 cents to cover transaction costs. (Some of those transaction costs could be charged even if the credit card is rejected, which means there may be multiple transaction costs for a single entry, or even transaction costs that never result in an entry.)
There may be additional bank fees incurred to get the funds to the organizer.
Designing a generic tournament entry site is not as simple as it seems, because there’s no such thing as a generic tournament. Are there multiple sections, and if so, are there ratings-based or age-based restrictions on those sections?
Can players enter more than one section?
If the event has multiple schedules, can a player enter more than one schedule?
What’s the cutoff for advance entries, and what’s the cutoff for ‘late’ entries?