Speak of the Devil by Christine Pope

Their supernatural talents could make them the perfect team — if Hell doesn’t claim them first.

Caleb Lockwood has a foolproof system for winning big in Las Vegas. Being part demon helps. Fresh from his escape from Hell, he’s looking to lie low and build a new life, starting with flipping a haunted house. Too bad his realtor has a knack for spotting supernatural trouble.
Delia Dunne’s business card might advertise “luxury real estate,” but her true expertise lies in cleansing properties of unwanted spectral tenants. When a casino executive hires her to investigate a streak of suspicious wins, she never expects her newest client — the charming house flipper with seemingly unlimited funds — to be at the center of it all.
From the moment Caleb and Delia step into a ghost-infested property, things get complicated: sparks fly between them, spirits vanish mysteriously, and demons start showing up with deadly intent. As Delia digs deeper into Caleb’s past, she uncovers a two-year-old disappearance, a rebellion in Hell, and a secret that could get them both killed. Worse, the powerful figure behind it all is closer than either of them realized — and he’s playing for keeps.

The stakes are high, the odds are stacked, and in Vegas, the house always wins. Unless you’ve got a quarter-demon and a ghost hunter in your corner.