The unit that is supposed to be sold would only be an off the...

The unit that is supposed to be sold would only be an off the plan sale. A deposit would have been paid, either a 10% payment or a bank guarantee for the 10%.
Nothing is sold until the building is complete and final signoff  and registration finalised and the balance of the purchase monies paid.
Otherwise its just cheap talk, I remember  years ago a developer had sold nearly 50% of this 40 odd units in this development.
Today 8 years later it sits unfinished as the buyers pulled out and then the bank pulled the pin.