It's variable. Most will do what you ask of them. We'd have the petsitter come by 3 times a day. This would include both meal times and my dogs could make it that time in between without an issue (7am, 1pm, 7pm). They'd stay for 1/2 hour to an hour as well to play with them or just keep the company. In addition, they'd bring our mail in. Most petsitters will do other little things like water plants or other minor things like that.
The last time I used a petsitter, it was $15/visit. The beauty of it is, if you have more than one dog, it's the same price for 2 dogs (like us) as it is for 1 dog because they are coming to your home. While you only have one, if that were to change, it's just another benefit. Your dog doesn't get stressed out being away from home. And you have someone checking in on your place while you're gone which is more peace of mind.
Go here:
Pet Sitters International
They will help you find one in your area. They also make sure they are licensed and bonded. Makes trusting them a lot easier. Otherwise, ask around and see if any of your friends have ever used a pet sitter and how they feel about them. It often ends up being old people that do it because they truly love animals and tend to be around during holidays. We had the nicest old couple that did it for us the last time. They loved our dogs and would end up staying even longer just to keep them more company even if it was just sitting on the couch with them and watching TV.