Or perhaps someone will casually glance through your credit card purchases or cell phone bills to find out your shopping preferences or calling habits.
分析主干：someone will glance…
本句是个简单句，谓语动词glance 后接介词短语through purchases or bills.不定式短语to find out…在句中作状语，表示“无意中一瞥”的结果。
译文：或者有人会随意翻阅你的信用卡购物单或手机话费单，以此来了解你的购物喜好或通话习惯。