I’m unsure how such a scam could be averted. The post office will vouch that it delivered a package, but can’t vouch for what was in it. Could your friend have insisted on being returned (even at his expense) all the packaging material and the “piece of wood”? Then he could have weighed it and compared it to the Post Office documented shipping weight, and if they were different, could have reported the case to state or (yeah, I know, ludicrously overloaded) Federal authorities.
Maybe take a photo / video of the item going into the packaging AT A LOCAL MAILBOX STORE. Or UPS store.
Also for expensive items ask for the signature upon delivery. That way the recipient can’t say the package was stolen from his doorstep as someone did with us (an XBox!). We had asked for signature and the idiot had signed it so we were free and clear.