"True Market Value" (TMV) is the price somebody is willing to pay for something at that specific time. What is the price of something that sells one month at $100 and the next month at $500? Whatever somebody is willing to pay at the time, that IS the "true market value" at that time.
Now, whether somone over or under pays RELATIVE to the most recent transaction, that is their decision.
The market price of a toy soldier is completely subject to the law of supply and demand. More demand equal higher price, and vice versa. If someone buys a toy soldier at a higher price than it went for recently, they must believe it is worth that. If someone decides to sell at a low price they must have their reasons for doing so.
Obtaining reliable pricing information in an opaque and illiquid market such as toy soldiers is difficult at best. The surest way is to offer something for sale and see what bids you get. If not to your liking, you can choose to accept what is, or hope for better luck next time. Of course sometimes time is of the essence and the seller chooses a "bird in the hand versus two in the bush".
At the of the day the toy soldier market is much too fractured and illiquid for there to be definitive market prices. Houses, stocks and bonds, gold coins, all these can be comparatively shopped with great ease. The price of a out of production toy soldier, not so much.
Individuals should have the right to buy and sell their toy soldiers at whatever price they like without taking criticism from the market at large. It is nobody's business but theirs.
Dealers who are going thru ebay to undercut set price lists from manufacturers is another story. But that is also is between those two parties.
After market toy soldier prices fluctuate, sometimes wildly. Those who seek to profit from such an unstable and thinly traded marketplace must accept the risk that the market will not conduct itself as they would like. As we all know, there is no return without risk, even in the happy land of toy soldiers.