I worked on this, it was called Milo.com. we had crazy scraping and xml/csv feed ingestion. It was a terribly difficult business because most retailers hated us. ebay bought it and eventually killed it.
Huh! Well thank you for your efforts! When was that? Do you think it would be possible to build it again?
Why did retailers hate you? Wouldn’t they want a solution that brings people to their store because you listed their product as being there and available?