There is much more to scalping than that, but that is one way. you can also scalp out a Match Play, or scalp out to get the most of a nice 50-100% bonus, where a 5c line will do the job.
But if you are looking to scalp just the games, yes, you need to have the dog be greater than the fav, for ex. +150/-145 this would be close to a 1% scalp.
BB