GrabHitch is a social carpooling service which is supposed to defray your daily commuting cost. You would already be paying for this with or without your GrabHitch rider for the trip.
Networking and chatting with your rider will definitely bring more value to your daily commute.
In cases where you have to enter an ERP zone just to pick up or drop off your rider, you may ask your rider to share the cost with you. Do check with him/her upon accepting the booking and not during or after the ride to avoid dispute.