I personally would keep the product offerings simple, catalog is catalog, first off if you make it opt in, not sure what buyer would say sure, take my offer use it to start your auction and I will wait 30 days. I would never click that opt in box, and I don't know who would ?
If you were so keen on an auction, start it as an auction, not a catalog listing that is a wolf is sheep's clothing. You started this whole campaign we are not like Go Daddy Auctions, we make things simple, keep it that way. Again IMO.