Body for Sale, by Richard Deming (epub/Kindle/pdf)

Tom Cavanaugh never quarreled about the means involved, just so long as the end was worth grabbing for. He was about to get fired when he blackmailed his boss into making him district sales manager.

Helen Mathews was no lily-white, either. She was rich, beautiful, and as coldly calculating and cruel as a jungle animal. When she learned her husband might kill her for her money, she wasn't frightened. All she wanted was revenge.

She let Cavanaugh sample her lush body and then made him an offer. For killing her husband, Cavanaugh could marry her and share her wealth.

Cavanaugh hesitated, but his decision was inevitable. He set out to commit the perfect murder.