I have 2 small dogs and I want to know if a sitter's pricing says $30 per night, will that be different if more than one dog is in the home?
Yes, the typical structure is price per night, per dog. You can ask the sitter if they offer a discount for multiple dogs.
For boarders, when you click on the 'services and rates' tab on their profile, it will show their nightly rate, plus their additional dogs rate if they have one set. While pricing ranges from charging nothing for an extra dog to charging more than the original rate, it seems the majority of boarders charge less for the second (or third..) dog than for the first. Traveling sitters don't have as many pricing options shown on their profile - they often handle dogs, cats, small pets, and other household tasks for their clients, so their rates are far more variable and all the travel sitters I know give individual quotes depending on the client's needs.