It came as a surprise to me to learn that in some parts of this country, custom dictates that the sellers remain in a house for an average of 30 days after the closing -- as tenants. Standard practice.

In most areas, though, a purchase contract usually dictates that occupancy is to be given at the time of settlement, on the day when the money and the front-door keys change hands.

Every situation is a bit different, though, and sometimes it's even necessary for the buyers to move in before closing. Brokers, and real estate lawyers, advise as strongly as they can against allowing that.

Too many things can go wrong. The buyers have time to discover every little problem with the property. Perhaps in the end they won't even obtain their financing, and what then? Who will pay for the window that breaks in the meantime? Whose insurance covers the house? Their belongings?

If the rent is set lower than their projected mortgage payment, will they stall about closing? And what if they never do close on the house and take their time about moving out? Will normal eviction procedures apply -- or won't they help?

On the other hand, there is occasionally the problem of the seller who needs to close but can't move out immediately. Often the sales contract, in that situation, sets a rent figure on a sliding scale. If they don't move out by the agreed-upon time, the rent will keep going up, until hanging around gets just too expensive.

It all points to the need for advice from an experienced real estate attorney, before signing any contract that allows the buyer to move in ahead of time -- or the sellers to remain once they no longer own the house.