So... an interesting development in the saga of the "Gulbrand Enger". It looks like Goodwill has since revised the listing to indicate the violin has not been authenticated. Many people have retracted their bids, and the violin's gone from $3,000 to $800 overnight.
I also sent a valuation inquiry to Brompton's, and they said that based upon the images I sent, they would place an initial auction valuation at 4,000 GBP. Of course, that's subject to change based on first-hand study.
It's been mentioned that the quality of wood appears to be lower than expected for an Enger, but -and I'm simply playing the Devil's advocate here- isn't it possible that since this was purportedly made relatively early in his career (when he was still learning the craft), that it's not made to the same standards as his later instruments?