I personally have NEVER encountered that situation since not many sellers can finance their home for the renter.
Homes are VERY expensive in this area so it's a different situation compared to other parts of the country.
Renting is only $2,500 (example) for this beautiful home which would sell for 800k (example; probably more!) Anyway, you would only have to put down a one month deposit to rent (security is usually one or two mos rent) and then the Seller would have to finance the rest. Why not just pocket the rent and then sell it ? If they are able to collect rent, it's a bonus and then if they are moving, it's easy for them to just sell it outright and have someone put down 300K and mortgage 500K. This is why I'm moving to PA! I found an incredible house for 250K and it's literally a $1M in this area of NY.
GOOD LUCK TO YOU!