I know that a sourcing agent can charge his clients by hourly rate, but I don't think it is a wise strategy. If a sourcing agent charges a percentage of each order, then he has to be in the middle, but what if the client cuts out the agent and does business with a manufacturer directly? Do you have any good ideas?
It depends if you have any applicable contracts in place and the resources to fight in the courts. You really need to speak to a lawyer about this and be prepared to pay for advice, contracts, etc.
On the other hand, you can just accept that this is what might happen and move on. If you have lots of clients, then losing a few won't matter.