The insurance companies we contacted all said having an unpaid house sitter would not affect the home owners home and contents policy, in fact they prefer to have someone living in the house as opposed to leaving it vacant. They said everything would be normal in accordance with the terms and conditions of the home owners policy. The only thing needing to be checked is whether the policy covers accidental damage as well as the sitters possessions. If a sitter is concerned they need to arrange their own insurance. If a sitter is being paid to house sit or is paying rent to the home owner then the home owners policy will be affected and separate insurance would be required.