Oxytocin, the love hormone, makes people more trusting of others, but it doesn't make us trust people we otherwise wouldn't. To determine this, men played a trust game. Some men inhaled a trust-enhancing oxytocin spray, and they proved more trusting of strangers than men who smelled placebos; however, when there was a reason to doubt others, like hearing a stranger had history of violent crime, both groups exhibited similar levels of trust.
Researchers concluded the love hormone won't delude us into foolishness. Yet suitors with a dubious history — say a past of violent crime? — don't exactly broadcast it on first dates. And while I don't have an hormone-sniffing study to prove it, I'd say it's hard to break trust once it mixes with lust.