Don't depend on your reservations in Vernazza. We made them and secured them with a credit card. However, when we arrived there was no record of our reservation. One of the workers there felt bad and offered us an apartment he had at the same price. It was fantastic and opened to the sea.
Sorry (I guess) for your misfortune. Sounds like it turned out OK, though.
I've been to Vernazza and Cinque Terre numerous times and never had this problem. I have also made reservations secured with credit card (though paid in cash after arrival) and always had them come through just fine. Stuff happens everywhere sometimes with no explanation.
However, I do know that just because you send off a reservation with cc, that doesn't necessarily mean you are confirmed until you receive a confirmation email from the property to that effect. Also, they generally want to know when you expect to arrive and with the demand in Vernazza, if you arrive late, it isn't unheard of for a room to be given away.
I try to always call a month ahead of time to re-confirm my reservations. I did this with our hotels for our last trip to Italy but failed to do this with our rental car reservation & when we showed up to rent our car in Orvieto, they had no record of my reservation & of course no extra cars to rent! I learned my lesson & will definitely re-confirm everything a month before leaving for my next trip!! Of course, there's still no guarantee that they'll honor your reservation when you get there, but at least it's a little reassurance!