Remember when Mom told you never to speak to strangers? Well, all that goes straight out the window when it comes time to sell your house—after all, you have little choice but to invite anyone claiming interest in your precious abode inside. It’s too bad some of those individuals may have nefarious intentions.

This week, a man pretending to be a real estate agent at times and a buyer at others was arrested on charges of stealing valuables worth millions of dollars from more than a dozen celebrity homes in Los Angeles. Benjamin Ackerman‘s alleged victims included singers UsherJason Derulo, and Adam Lambert and “Real Housewives of Beverly Hills” cast member Dorit Lemel, according to the Daily Beast.

The con man got access to these luxe homes by pretending he was a real estate professional hoping to show the property to prospective buyers. He also reportedly attended open houses.

Should home sellers be on their guard at all times?

“You’re inviting complete strangers into your home, and you don’t know what their motivations are,” says safety consultant Robert Siciliano, CEO of Safr.me, a Boston-based firm that provides training for homeowners and real estate agents. “You can’t just trust that anybody you’re going to invite into your home is going to be legit.”

Don’t panic! Just take the following precautions, say security and real estate experts:

Remove or lock up your valuables

Most legit real estate agents will advise sellers to lock up or remove anything of value—including jewelry, watches, expensive artwork, and even prescription medications. And they shouldn’t hide ’em in underwear drawers. Instead, buyers can invest in a safe, lock items in a closet, or drop them off someplace safe during showings.

“That’s just common sense,” says Siciliano. “You need to be proactive.”

Verify the credentials of prospective real estate agents

Just because someone claims to be a real estate agent—or a buyer, for that matter— doesn’t mean that it’s true. Anyone can order professional-looking business cards adorned with fake titles and company names. Some thieves will set up fake websites, or will even have friends pose as references. So it’s up to sellers to be thorough in their background check.

To eliminate potential scammers, Siciliano recommends contacting their offices and asking a few questions, looking them up online, and checking their social media accounts to make sure everything seems kosher. Sellers can also ask for the individual’s real estate license number or other credentials.

Folks should also trust their instincts.

“If something feels wrong, something seems wrong, it probably is wrong,” Siciliano says.

Watch prospective buyers and agents carefully

When possible, sellers should keep prospective buyers and unproven agents within sight. The more expensive a home is, the more it becomes a “high-value target,” says Siciliano. He’s seen sellers hire private security details during showings.

To be on the safe side, New York City real estate agent Ian Slater, of Compass, will often schedule only one couple at a time during open houses for pricier listings.

“We’re very cautious about this,” says Slater. “I’ll personally accompany every single person through every single room.”

Don’t leave personal photos or mail lying around

Homeowners should make sure there aren’t personal pictures, bills, or correspondence visible during showings. Identity theft is not part of the deal.

Check your homeowners insurance

Some homeowners insurance will cover property stolen during an open house or home showing. So check policies before putting your home on the market. Document everything before the selling process starts, shooting photos and videos within the home before it gets opened up to viewings. It could pay off down the line if anything goes missing.

Clare Trapasso is the senior news editor of realtor.com and an adjunct journalism professor at St. John’s University. She previously wrote for a Financial Times publication, the New York Daily News, and the Associated Press. She is also a licensed real estate agent with R New York. Contact her at clare.trapasso@realtor.com.