I agree with @KC1102. Based on my experience being asked to contribute towards utilities is very rare. In all my sits, including multi-month sits in cold winter places and hot summer areas, I’ve never been asked to chip in.
I have seen some listings that mentioned wanting sitters to help pay the utility costs. And there are situations where some sitters may be willing to chip in on the utilities. Here’s a thread where some sitters talk about times when they’ve chipped in and why they were ok with that.
The bottom line is all requirements must be agreed to prior to the sit being confirmed. Communicate, communicate, communicate.