The value of a stein is determined by what someone will pay for it in the market place. If someone buys it for $45, you can assume that the value is at least $45. You can watch ebay, the world’s largest market place, to see if you stein comes up and what it sells for. Or you can put yours up for sale on ebay for what you think it is worth. I have seen one stein on ebay that started out at over $2000 years ago, and is still for sale around $800 now.