If order total > USD300 then provide only
eCheck payment method.
This is required by opencart store owners
if the number of cache back
requests from credit cards is increasing. It also decreases the risks of fraud orders.

Can be easily customized to allow other payment methods like COD for example.
The idea is to stop many clients to add lot's of orders and then have great risks of getting requests
to return the money back from bank if any client request if via their bank.