Here's an image of the stamp from the above
ebay listing:

Let's assume for a minute that the cancel is real ... if it is, then what type of cancel is it? The diameter seems too small for any US cancel that I recall seeing.
Can anyone make out the smeared wording within the cancel?
Wouldn't there be a date included in any hand cancel such as this?
As khj suggested, someone would have to be "an idiot" to cancel a mint block of 4 of these stamps given that the price of a used block is only a fraction of one in mint condition.
Does anyone seem to think the perforations look a bit off, or was that normal for this early issue? (I am particularly noticing the center vertical perforation in the bottom two stamps.)
Not that I have any interest in purchasing this particular item, but it just looks so unusual, I'd be interested in any further comments about it.