Tom and Sarah Kotowski got all the turnout they could have hoped for at their open house.

Close to 100 people showed up last Sunday to take a look at their three-bedroom Cape listed for $299,900 on a quiet East Weymouth cul-de-sac. Four made offers. By Tuesday, the couple had an agreement.

“For a seller, it’s excellent right now,” Sarah Kotowski said. “Inventory is flying.”

But as the couple looks for a home closer to Tom’s workplace west of Boston, they face the same dynamic.

“I can’t tell you how many open houses we go to and then the next day they’re gone (off the market),” Sarah said.

The strong seller’s market that has emerged this spring is a double-edged sword for families like the Kotowskis, whose house was on the market for less than a week.

Home prices are rising across Massachusetts this spring in a reflection of demand that is outstripping supply. There are fewer than 20,000 single-family homes on the market, down 30 percent from