How do rules of thumbs work?

[Anthony Z.]

Hello there,

I am brand new to real estate and I am going through the free course that BiggerPockets provides. I was going through Module 5: How to Find Real Estate Deals and it teaches various rules such as the 2% test, the 50% rule, and the 70% rule. 

My question is, if everybody is using these same rules of thumb then how is there any property to purchase? Doesn't a property that passes all these rules indicate that the seller is doing something wrong? And if everybody is using the same rules then wouldn't everybody be trying to buy the same properties?