... do I think they would lose a deal over $500? No. ...
Maybe it depends on regionally, but the reality I'm seeing is this: the US ID.4s are being built for customer orders only. Maybe that's no longer the case, but many dealers are happy to be in possession of your "customer refused delivery" ID.4 because whereas they are directed by VW to sell it to the original ordering customer at sticker, they are free to mark it up once it's for sale on their lot. And many of us have seen ID.4s marked up $2,000 to $5,000. Is anybody actually paying that? I don't know (nobody is going to post on this forum that they overpaid). But point is, the dealer has more freedom to mark up the selling price once the original orderer is out of the picture.
That's why, as a dealer, I'd be happy to honor a request for a small discount up front to get business, in the hopes that a bunch of ID.4s land on my lot, and some become cancellations. Then I could make the discounts back plus some, increase my sales volume, and actually have product to sell with this constrained supply situation. But once that vehicle is in transit, I don't see the incentive to adjust price.
Again, try. Others have and have saved some cash.