Like our laws, valuations are usually based on precedent, - listen to anyone on the Antiques Roadshow and they will probably say something like "one of these was sold for...". This is how we arrive at a value, by looking for previous sales of the same or similar items. I'll let you into a secret...it's not hard once you have identified the item. Once you know what to look for, an Internet Search will provide back catalogues from such specialist auctioneers as Mullock's. Similarly, the Advanced Search on EBay allows you to look at completed sales, again providing an insight into what people think an item is worth. You can also search retailers web sites, but be aware that the sort of price an item can command in a retail setting is not what you might be offered should you try to sell. "The price of a second-hand item is inversely proportional to the number of people who will pay it..."
Having said this, one of the things I do enjoy, and am happy to have a stab at, is the identification of items. The quality of photos possible with a Smartphone today would have been the envy of hobbyist photographers a decade or so ago, and sending images has become part of our culture so in real terms it's never been easier to get stuff identified, so please send your puzzles...just don't ask me to tell you what they're worth!