I dare say that most of these ads are scams. I see them too, especially on Craigslist. I've never really warmed up to the rent-to-own properties because more often than not, they make no sense.
The only reason a buyer would want a rent-to-own is if he or she was unable to obtain a mortgage. Most sellers I know would only consider this set-up if it is a person with good credit and money down. So, where's the advantage? It would make just as much sense to go for a property where the seller is offering to finance the place.
I saw rent to owns as more popular a decade ago where sellers had equity in their home and perhaps they were not having success selling their homes. Today, at least 30-40% homes on the market are either short sales or foreclosures, so this type of of thing isn't even an option. In addition, there isn't enough inventory compared with buyer interest, so rent to owns have really dried up.
I have a really good mortgage broker I'd be happy to refer you to Stephanie! Just get in contact with me if that would be helpful!