MindMyHouse works by bringing home owners and house sitters together. What home owners and house sitters agree to after they have made contact is often private and we are not always privy to that information. If you have particular expectations (eg. payment, food etc), it's best to ensure that you can communicate your expectations with the home owner before you agree to house sit for them.
That said, house sitting is usually a free exchange of services (ie. looking after the home owners' property and/or pets), in exchange for free rent. Some house sitters may charge for their services, but generally most house sitters will provide it for free, in exchange for free rent.
Also, some home owners may expect that you pay for utilities, others may not. Some home owners may also require you to do some jobs around the house/gardening and/or pet care, and others are more in the line of caretaker positions. Ultimately, we leave it up to you and the home owner to negotiate.