This might be dependent on the country in which the transaction takes place. Under some circumstances, if Bob believes that the laptop is now his, it actually is his property in some legislations.
For instance in the Netherlands if you believe the person selling you the item has the right to sell it to you // perform that transaction, its yours. (The so called 'Vertrouwensbeginsel')
The only way for Alice to get her money back would be by going after the scammer, because he did not do his part of his deal with her(paying).
It should be noted that the belief should fall within reason.
So if something about the transaction is completely and obviously fishy, i.e. 'you should have known something was wrong'. Then its impossible to invoke the 'vertrouwensbeginsel'.
