A percentage of the first year salary is quite normal in the UK. Usually going to £0 if the hire doesn’t pass their trial period.
The percentage is a negotiation point.
negotiation point for whom the recruiter or does the recruit actually know about the numbers?
If the recruiter wants your recurring business then they’ll move their percentage to be more favourable for you.
I’ve got 10% rates in the past. Always negotiate.
The usual recruiter fee for regular mid-level employees is less than 25% but it's highly variable and negotiable. The fee can vary a lot depending on how hot the market is and your volume of business.