I think that one never has the right to negotiate after the fact. You can accept and shut up or you can return the object. Those are your only two options. If the seller then prefers to offer you a discount rather than accept a return of the item, that is up to them but you have no right to bring up the topic or insist on anything.

It is furthermore always the responsibility of the buyer to be aware of what they buy. Old bike values are made up of two elements: the usable value and the collectible value. The winning price that you paid was based upon the overall knowledge of all the potential buyers out there. I can assure you that others who did their homework will have discounted their bids to take into account the need of a repaint to be able to bring the frame up to snuff as far as collectibility goes. As I said, the bike is fully usable as is and therefore has not suffered any depreciation in its usable value due to the paint. The non-original paint has already hurt the collectibility value to such a point that one had no right to claim any added value for collectibility. So if you as a beginning collector are bidding on a bike thinking that it has a certain collectibility factor, it is your responsibility and only your responsibility to know how to evaluate this correctly. Like I said, you were the one who decided to play with the big boys and assign an added value to this bike for the fact that it was a Cinelli and not some other less desirable frame, you must therefore be big enough to recognize that you are out of your league and were not sufficiently knowledgeable to play this game.

If this was the bike on German ebay a while back, I remember it quite well and had no problem at all to discount the overall value of the bike to be that of a no-name Italian frame in rideable shape with a 50th anniversary gruppo. No more no less. If it was indeed that bike, you got a price that was fair but far from a screaming deal.