This is a classic example of how 99% of users write, which is not constructive:
https://forums.d2jsp.org/topic.php?t=80163454&f=100For usual items:
1) Search up the item in the search field. If you find threads with the item sold or offered prices, copy the links and paste it to the price check thread with some description.
2) If you find no threads, write exactly that: There is no previous items like this openly sold, so you can try with a price you think is fair if you want to sell it.
For unusual items:
1) If you have experience with similar items in the price check thread, don't be afraid to share that knowledge. Usually these items are diffuse and difficult to price check, but in the pvp scene, these items usually goes "under the radar", i.e. through pm, but it would be unfair to not share that knowledge. Who knows what delicate items went out of the world of D2 because of lack of will of knowledge to be shared?
2) Comparing rare, crafted and magic items with unique items can be a good way to decipher a realistic price.