Other tablet owners are listing their hardware on the site, too, said David Pederson, a spokesman for the company. "Inquiries for all other tablets -- Kindles, Nexus 7, Nook, and so on -- were up 35% [last week] versus the week before," said Pederson in an email reply to questions. "Google's Nexus 7 saw the biggest gains with a 300% increase in inquiries."

The Nexus 7, which , is a 7-in. device priced at $199.

Nexus 7 owners, however, may not be selling their tablets to buy an iPad Mini, but in the expectation that Google will take the wraps off new models of the diminutive tablet, as well as a reportedly made by Samsung.

The escalation in trade-in activity prior to Tuesday's event has been much less pronounced than seven months ago, when owners stampeded to sites like Gazelle and NextWorth to dump their older iPads before the launch of the Retina-equipped "new" iPad, called "iPad 3" by many, if not Apple.

Then, in quote requests compared to the month before.