Not true. This is from the Wikipedia page "Possession of Stolen Goods":
Possession of stolen goods is a crime in which an individual has bought, been given, or acquired stolen goods some other way (other than they themselves having stolen them).
In many countries, if an individual has accepted possession of goods or property and knew they were stolen, then the individual is typically charged with a misdemeanor or felony, depending on the value of the stolen goods. If the individual did not know the goods were stolen, then the goods are returned to the owner and the individual is not prosecuted. However, there are often exceptions, due to the difficulty of proving or disproving an individual's knowledge that the goods were stolen.
There are then several sections detailing the laws in different countries, but under the United States heading is this:
To be guilty of the offense, a person must know that the property had been stolen, but he need not know that it was moving as, or constituted a part of, interstate commerce. The term "interstate commerce" merely refers to the movement of property from one U.S. state into another; and it is sufficient if the property has recently moved interstate as a result of a transaction or a series of related transactions that have not been fully completed or consummated at the time of the person's acts as alleged.
It is beyond impossible for people to know which things they buy are stolen and which aren't. If an owner of a convenience store steals a crate full of tampons and sells it in his store, there's no way a consumer could determine that. Cops aren't going to arrest some woman for buying stolen tampons. Are we supposed to ask everyone we buy anything from where they got it? They're not going to admit having stolen it even if they did. So are we supposed to trace every single thing we buy back to its source? Good luck with that.
One might suspect that something is stolen, particularly if it's something cheap on Craigslist, but there are plenty of legitimate deals on Craigslist for non-stolen goods. We have no way of knowing and we have no responsibility to find out. If the dude says, "Hey, want to buy some Legos I boosted from a delivery truck?" THEN you're committing a crime by purchasing them.