You can tell the gold guide users on the AH though. When you are posting things up, if you are the only one and you put it up for say 1000g. Next time you go to post it might tell you to put it up for 1050g, then 1100g. Then 1200g. etc, ad naseum. It doesn't stay the stay it keeps adding the price till it is WAY out of whack with anything reasonable. Still it's pretty good for posting up stuff so long as you know the price already.
Often the name modification (or "mod" for short) is used interchangeably with AddOn. More specifically, a mod is a third-party AddOn that alters or enhances some aspect of the game's interface. Mods can perform a wide variety of tasks, including adding new buttons to the screen, altering the built-in player and party frames. In extreme cases, mods completely supplant the standard game's interface, usually offering more advanced functionality.