Anything's possible... likely? No, it will take you millions of years to find a block on average. As for why they sell them to you, it's because it's easy to sell hardware to people who don't know what it is they're buying if the sales pitch is all bullshit.
I bought on Amazon UK, And sales pitch was that I could earn at least 25 bitcoin per month. If that's really not true I will raise an issue with Amazon
Ouch that is straight up BS I'm sorry. I own one erupter and I've thought about plugging her in for a minimal chance of hitting a block solo. Try it out, it's worth a shot but don't expect it to happen.