In General: Generally, a dog owner is only liable for damages to a victim when they knew their dog had dangerous propensities. Dangerous propensities generally means if the dog had previously attacked someone or if they displayed dangerous and aggressive tenancies. It is important to thoroughly research the owner to find if the owner had previous citations for animal attacks or was previously sued for a similar claim.
Strict Liability: In some jurisdictions, a dog owner is strictly liable for the injuries their dog causes. This means that the dog did not previously have to attack someone or display aggressive tendencies for the owner to be held liable. While there are exceptions, they are relatively narrow and limited, and, in many jurisdictions that use this strict liability standard, the issue of liability will usually be minimal.