We usually have the potential sitter over for dinner and have them feed everyone (3 dogs, 2 of which cannot be in the same room, 2 on meds; a cat on meds; fish and frog tank; and chickens) while we are there to walk them though everything including keeping the 2 dogs apart. From that, we can usually tell if the critters are going to be in good hands. We always call in the mid-evening of the first night that the sitter is there to see if they have any questions and to get a report. We write everything down (names and descriptions of pets; feeding schedules and amounts; vet number and directions; how to get in touch with us; trash days; etc.) including a check list of what has to get done daily. If we are gone more than a day or so, we have the sitter move in.
As for paying sitters, I usually find college students or people just starting out who are living in at home, in a group situation, or in a cramped apartment. They are quite glad to house sit where there is cable, food in the fridge, and some privacy. People in these situations come cheap and do a good job so that you will ask them to do it again.
Good luck.