A bump clause lets sellers enter into a contract with a buyer while still continuing to market the property. If the sellers get a better deal, they can “bump” the original buyer.

It’s most commonly used when a buyer’s offer has some contingency, usually that they need to sell their current home first. It can help coax the sellers into contract by offering them the ability to seek alternate buyers who don’t have a home-sale contingency or who are offering higher prices.

The clause tends to become more popular in markets that are “transitional,” where once-hot home sales are cooling but sellers haven’t yet adjusted their expectations. The tactic can be “a savvy technique” to help the sellers feel they could still get a better offer, says David Reiss, a Brooklyn Law School professor who specializes in real estate.

If the sellers do get another written offer they want to take, they must notify the original buyer. The buyer then typically has a few days to tell the seller they’ve sold their house, or that they’ve decided to waive the contingency. If not, the original contract terminates. The original buyer gets back the money they put down, and the sellers enter into contract with the new buyer.

The sellers can only keep marketing the property until the buyers satisfy or waive the contingency. So once the buyers notify the seller they’ve sold their existing home, the seller’s right to market the property ends.

Rebekah Carver, a real-estate broker with Douglas Elliman Real Estate in Brooklyn, N.Y., says Brooklyn has been a hot market for a long time, and bump clauses haven’t been common. But now she’s representing buyers on a deal where the seller had resisted signing a contract with a home-sale contingency, even though the property had been on the market for about six months. Ms. Carver offered the bump clause to try to put the seller’s mind at ease.

In general, the bump clause can “give the seller some sense of security and comfort,” says Ms. Carver. The bump clause can be proposed by either the buyer’s or seller’s side, but is often offered by the buyer’s agent as a way to get the seller to accept a contingency.

Robin Sheridan, a real-estate broker with Realogics Sotheby’s International Realty in Seattle, says that when she is representing a seller facing a home-sale contingency, Ms. Sheridan often does her own due diligence. “I want to be certain the other property is one that will sell quickly,” she says. “I vet the buyers via their lender and ensure all their ducks are in a row to navigate the two nearly consecutive transactions. Knowing the bump clause is a possibility is comforting to a seller, but most of my clients remain firmly committed to the contract in hand.”

Here are some things to consider with bump clauses.

For sellers:

• Use it as leverage. Since the house is already under contract, a seller can use the clause as a negotiating tactic with any other buyers that show interest. The seller can try to get the other buyers to outbid the current price or negotiate a contract without contingencies.

• Don’t get greedy. If the seller receives a second offer, he may be tempted to “bump” the first buyer and sell to the second. But sellers should make sure the second offer is at least as strong as the first, which means looking deeper than price and contingencies. The new buyers may have poor credit, for example, and be less likely to obtain a mortgage. “It’s a bird in the hand,” says Mr. Reiss. “If they walk away and are stuck negotiating with a second offer that’s weak, they could end up with nothing.”