Someone has mentioned to me that stock rims can't be balanced "normally" due to the absence of a certain "cup" that allows to put the wheel onto a balancing machine.
If there's no centre bore then most tyre shops can't mount the wheel on their balancing machine. They all used to have adaptors to do it but most tyre places don't have them anymore. Shop around though, you might get lucky. For example a JAX near near me randomly had the adaptor because the owner was a former Peugeot tech!