Types of Online Scams

In my opinion, avoiding scams or having the ability to recognize them might be as important as being able to recognize legitimate opportunities. Scams will either just waste your time, or time and money. I will try to give a few examples:

-Programs that will not require any payment or deposit, but will never pay you for their work even if you reach the minimum payout.
-Programs that will not require any payment or deposit, but will not pay you because you did not reach the minimum payout. The scam here is that the minimum payout is so high, that taking into account the pace in which you earn money, it could take you a year or more to accumulate such an amount of money. During this year you might stop being interested in earning money online, the company can stop existing, or it can have financial problems and will never pay you. It requires some experience and knowledge to spot such scams.
-Programs which require a purchase of an attractive product, which is supposed to make you money. It may be a pyramid scheme or something else. Into this category I would also include websites that charge a membership fee before you make any money. It might be called a business start-up kit. What all of those programs and websites have in common is that you are not going to earn any money because of them, but rather waste your time and money.

What are your thoughts on different type of scams? Which are the most dangerous?