I will take some examples straight from the Official Price Check Thread and walk you through the process that I personally go through when pricing these items.
Example A:
Price check on Pirate Meerca Morphing Potion. I have a feeling the prices on TP are too low. Maybe not?
What I am going to do first is go to our item DB and look up the price of all the pirate morphing potions to compare them.
Now that I have learned roughly what these can be bought and sold for in relation to the rest of the MPs, I will look on Neopets to see what they are going for at the moment:
I can stop here, I have my answer. If I want my potion to sell, I will have to price it lower than 200k NP on the TP. Pricing it at 99,999 in my shop would probably offload it quicker and with less hassle. Alternatively I could hang onto it hoping that the price will go up after the cheaper ones sell (protip: this rarely works out the way you want it to).
I always scratch my head when I see people ask for price quotes on items like this. They are not super rare, there are plenty of them on the TP with prices, and they are not newly released items. TRUST YOURSELF! You already know the answer
Example B:
Kadoatie Biscuits?
Unpriced on the TP and here
Ahhh, more of a challenge, an unpriced item. Just to be sure (not that any of you would ever overlook this) I will double-check our iDB and the Neopets TP to be sure that there are no current prices on this item at the time (which there are not). Next thing I will do will be to go to JellyNeo's Item Database to find the rarity index of the item and when it was released.
This will put this item in a predictable price range somewhere around 200-500k. Higher rarity gourmet/kad foods can get into the millions but they are HTS and you will probably end up deflating them anyway. If the item was super new I would put it closer to 700-800k but since these items are meant to be consumed people don't tend to pay ridiculous amounts for them unless they are crazy rare or collectable.
Example C:
Can I have the price for a :
Worn Leather Yurble Belt. Can't find a price and got it through a Treasure Map
Keep in mind that this PC was requested on 2 June, 2012. Checking the Neopets TP and our iDB turns up nothing, so off I go to JN again...
Because this item had just been released in the last couple of days, scarcity will artifically inflate the price to around 700-800k. Once more of them become available, some different factors will come into play. It is a less popular species, it's a belt, and it's not super high rarity - I would predict that it will be worth ~200-300k in a few weeks.
I would encourage everyone to attempt to price the items yourself before asking for a price quote from the forum. The more you do it, the more confident you will be in your own pricing abilities. If you do happen to price an UB incorrectly, it is not hard to figure out. It will either rot on the TP with no offers (priced too high) or you will get a handful of offers immediately (priced too low). So don't be scared! Just jump in and start pricing
If you have any questions or suggestions please let me know!