Everything associated with a real estate contract is negotiable. The fact that a written form is used does not mean that any or all terms of the agreement are not subject to modification.

Contract modifications can be made in two ways. First, wording in the original document can be revised directly on the contract form. Second, language can be added to the sales agreement. Such additions are commonly called "contingency" clauses.

The number and variation of contingencies are unlimited. There are, however, a number of owner-oriented contingencies with which a seller should be familiar.

Financing: The seller may require a buyer to obtain a financing commitment by a specific date prior to settlement. This is important if settlement is more than 45 or 60 days ahead. Suppose settlement is scheduled in 120 days and the buyer does not obtain financing despite a good faith effort. Many contract forms would provide that the buyer's deposit should be returned in this case. The seller would then have to market the property again at great cost and inconvenience.

Past Home: Buyers frequently want to sell a present home before being committed to a second. Sellers should take care not to be dependent on the sales appeal of the buyer's property. A contingency should be developed that permits the seller to continue marketing the home and, if a second buyer is found, provides that the first will have 72 hours to close the deal or withdraw without penalty.

New Home: A seller may wish to seek a new home even as the old one is sold. The contingency here would provide that the sale of the first home would not be completed until the sellers had found a second property.

Back-Up Contract: Sellers may accept more than one offer providing they have a contingency clause which states that no agreement shall be binding until a written notice of acceptance is provided. Such a contingency would state that the contract is back-up agreement subject to the acceptance or rejection of other offers.

Rental: If a house is sold in February but the sellers do not wish to move until June, there may be a problem of possession. If settlement is in March who occupies the property until June? A contingency can be used that allows the sellers to rent the house for several months at a set rental. Many buyers want such a clause so they will have time to sell a first home or for other reasons.

Peter G. Miller teachers the course, "How to Sell Your House - With or Without a Broker," through the Consumer Information Institute here.