I just it depends on how they screen their sitters (I would be asking very specific questions and I would also want to meet the person beforehand). DD is in Family Day Care so we've always asked for carers that are happy to do evenings on an occasional basis - which is a lifesaver as we don't have any family here.

Another good arrangement is to find a friend with the same child configuration as you and take it in turns to have each others's kids.