If it's too good to be true, it probably is. This is a statement that a lot of people know and use when dealing with scams. It works most of the time, but there are some that want to feel like they're special/lucky and found/approached by a good deal. I think these are the ones that are scammed more easily.
Another saying that I like to keep in mind is: You can't win a lottery if you didn't buy a ticket. So anything that tells me I won something when I don't remember joining anything, makes me think that it is a scam outright. And for those thinking that one can find a winning ticket along the road, that is the scammed mentality I want to avoid.