Electronics frequently fail at the beginning or end of their life, so if you put it through its paces, you should be able to detect a problem within the 90 day period. Also, depending on the reason for the reconditioning, there may have been little wrong with the unit in the first place; either way, it should be up to spec by the manufacturer when purchased in this way.
I was able to view the "New Product Warranty" info from the Denon website
here (it'll link to a PDF). Looks like it's two years for A/V receivers, so there is a difference there.