"Wanna buy an Ipad, for only $50?" Question about theft and handling stolen goods.

Where, for you, lay the boundaries of thievery and/or handling of stolen goods?
Where it says Ipad you can fill in any other goods.
1. You see an unattended Ipad in a coffee shop; do you nick it?
2. A thief offers you an he admits stolen Ipad ($50); would you buy it?
3. A colleague offers you an Ipad ($100), he doesn’t know the source, just that he bought it from somebody for $75; would you buy it?
4. An Ipad is offered for sale online, for $150, no details are given; would you buy it?

1. No, 2. No, 3. no, 4. Maybe…