(In addition to the PR problems, there is an additional issue: of all the towns of South Lebanon, the ONLY ONE that can ring a bell to many people is Canna, because it's supposed to be the place where the Christ changed water into wine)
First hand, a consideration. If QANA is an hoax, this will backfire on the Hezbollah. If QANA is real...well, the IDF should be very cautious in promoting the hoax hypothesis.
I guess the core issue is about wether the building collapsed immediatly or after seven hours. Is there any proofs of this ?