For Rent (for now) also For Sale (construction, renter, fees)

[ElGuito]

I thought about 10 days would be enough to find a rental place.
But still nothing.
Something the Realtor told me confused things even more.
He says a property can be for Rent, and will accept a 1 year rental commitment, but at the same time it is For Sale, so if it sells, say 4 months down the line, the Owner/Renter can nullify the Rental Contract and the new owner can ask You to vacate ipso facto. Is that possible, legally I mean? Even if both sides agree to nullify the contract without fees or penalties, isn't there some protection for the renter, on having lead time to vacate? Does the new owner have that right?
So the Realtor, suggested (not advised) not to consider For Rent/For Sale, which left Us only with a couple of Duplex types, OK area in Palmetto Bay, but older construction and not necessarily under surveillance by the building's security.