When Marty Ummel realized she had paid too much for her home, she decided to take action: She is suing her realtor.

Real estate lawyers and brokers say the case, which goes to trial in North County Superior Court on Monday, is likely to be the first of many in which regretful or resentful buyers seek redress from the agents who found them a home and arranged its purchase.

“When your house appreciates $100,000 in the first six months, you’re not quite as concerned that maybe the valuation was $25,000 or $50,000 off,” said Clifford Horner of the law firm Horner & Singer. “But when your house goes down, you ask: ‘Who might have led me astray here?’”

Ummel says agent Mike Little didn’t disclose “that similar homes in the neighborhood were selling for less because he feared she would back out and he would lose his $30,000 commission.” But Little says Ummel isn’t taking responsibility for her own failure to do research before purchasing the home.

Who’s at fault here, and what obligations do real estate agents have to their clients?