Auction House Help

recently i’ve been trying to get into the auction house scene to be able to make a little bit of gold but im not sure whats selling or good or whats dropping, how do people ususlly find the value of an item. i have many items that’ll say selling for like 4k gold and on the ah it’ll be 3 or 4. if there are any useful addons or maybe im just not doing it right, i would much appreciate some kind of help so that i could have a better understanding of the auction house, thank you. (ps, i am using undermine journal and tsm with all the addons for both addons)