That was something we were thinking about when renting our house. Been here over seven years (longer than I’ve ever lived anywhere in my entire life), and when we asked them about selling it to us earlier this year, they first said yes, but then decided against it. 🙁
It’s always a good idea, IMHO, because you will know for sure if you like the house, neighbors, and particular location. Additionally, you don’t have to move! It can save the seller tens of thousands of dollars by selling direct, too, so everybody wins! 🙂