I have not found a Real Estate company in Krakow which will get the rent from tenants like in the US and directly pay the landlord ,
in Krakow they usually charge 10% of the rent just to find a tenant which is quite easy and manage repairs but that's about it.
Do you know if such service exists in Poland?
I assume you mean as a tenant. I always negotiate here. The most I ever paid was 50% of what the agency initially asked for. Of course if the market is red hot there for real or your employer is paying, then maybe that's discount's not possible or not of consequence.
To the OP, I think 10% of the rent may be standard but haggle for a better deal with other agents.