Flooding In Howard Beach
Yes, there was some flooding in that part of NYC after TS Sandy, and it is entirely possible this machine could have been exposed. But then again so could any number of appliances sitting in basements anywhere in this country. You really wouldn't know until a close inspection was done, would you?
As for "CAVEAT EMPTOR", well that applies to any purchase of a used item from automobiles to appliances and all in between. Again one really doesn't know what one is getting until a close inspection and testing is carried out. Since the item is being offered on CL with local pick-up only one would assume a prudent potential buyer would examine the item closely or otherwise look for any possible damage including that from water.
Finally as can be seen from the photographs in the following link not every home in Howard Beach was submerged to the rafters, nor even to the ground (first) floor. Depending upon where this machine was kept (kitchen in a multi-family building, laundry area of a decently elevated house, etc...) it is quite possible nothing happened to it at all.