An item becomes rare when the number that are produce was smaller than number of individuals that desired the item. That sounds like something that should be simple to figure out, but there is a lot of randomness involved. Just a few things to mix it up can include:
- A so-so toy could become a central figure in the story/cartoon raising the status significantly.
- A so-so line takes off and the first run items are sought after.
- An unforeseeable problem at the factory resulting in a toy production run that was significantly cut back.
- Only one of toy X is included in a box while everything else get two (short packing).
- Only after most of the toys come out it is clear the toy X is the best.
- The line is cut early to make room for the next line and the last toys are sold/disposed in unusual ways and not sold at the typical retail stores.
- The fan community goes insane over one particular toy for random (maybe nostalgia) reason.
Given all of this you would think that online stores that have data to be able to predict some of this would be jumping over themselves to help you be notified when it looks like something is going to be rare so you can buy it with them "right now". But oddly that isn't the case (yet).
But besides the above mostly unpredictable cases stuff released at the end of the line is one situation I have seen that results in value/rarity it is limited to toy lines either. For many comic books as the series progresses the print run gets smaller and smaller as less people pick up each issue. Later when trying to collect all of the comics in that run it wouldn't be a shock to find later issues are more "valuable" simply because there are less of them. This seems to be a pretty universal truth and a basic economic story. People tire of the shiny new thing and move onto something else. Stores that want to move out the old line in preparation for the next line don't order more stock and the number of items produces later in the line can be much smaller especially at the end.
In the transformers world this stands out even more for a number of reasons.
- Typically every toy gets repainted at least once. The toys at the very end of a line are simply repaints of toys the buyer probably already has that mold.
- If a buyer had to choose between the two paint scheme often the first paint job is the cooler version.
- The toys at the end of the line are rarely if ever main story characters, at best they are in a single episode of the cartoon and at worst they are simply a character from the overarching universe.
- Collectors that had picked up every toy in the line might not take the extra effort to hunt down these because even if the toy is interesting the hero toy from the shiny new toy line is right around the corner and takes the collectors dollars.
These last toys are always difficult to procure in person, but can usually be ordered online for only a few dollars more than retail, well worth it because even online they sell out quickly so pre-ordering is a must. The toys at the end of a line have their own appeal. Not only are the cheap and easy to acquire with a little forethought, but they often become rare and valuable quickly. They also make for a very interesting and unique collection by themselves. When people post there collection photos it is amusing how many "complete" collection will be missing all of the toys from your little end of the line shelf.