A rip-off (also a verb) is "a product or service that is overpriced or of poor quality." It can also refer to theft or exploitation. Basically, if you think you've been taken advantage of in a financial sense, you can call it a rip-off.
Lots of people feel like they're getting ripped off when they open a bag of chips or cookies:
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I often feel ripped-off in restaurants here in Buenos Aires.
On my last vacation I took a day tour that afterwards felt like a rip-off for the price I paid.
What's the worst rip-off you've ever experienced?