The so called value can be fixed as well by whomever is doing the appraisal. Such a thing might happen as a favor to the museum. I hope its not the museum itself that is having the valuation done - that would be outrageous.
The hoard, which was valued at 3.3 million pounds ($5 million) http://www.freerepublic.com/focus/f-news/2549089/posts