I've found that value can vary from person to person and there are no set rules for value of a pin.
Some people go by original price, edition numbers, series, eBay listings, PinPics wants/trades, which park from which the pin originated, and many other factors including sentimental value and whether or not it has specific characters.
Ultimately, you must decide the value of a pin for yourself. We've had limited edition pins sit in our books for months, because the character is not popular, so it may eventually go for less than what a similar limited edition, with a hot character, may go for.
As MASTER said, you have to watch and learn and eventually you will get a feel for which pins will move and which pins will sit. It's all part of the game 🙂 Enjoy it and don't stress out too much about perceived values.