because i am in the process of buying the condo unit, despite being vacant, this seller wants the last drawdown onli willing to give me the keys - cos she wants everything according to the law

so, i am afraid if the day come closer and if i have no place to move in, i got to rent fr her the place (although the transfer might have done, but the money not yet reach her), i wonder if legally, if i sign the agreement on the spot (which also means start date of the agreement) and pay her with a cheque on the spot, legally, it means I can get keys?

thank you