[Googi]

The third and fourth suggestions make sense. The first one does not. How do you scale for items like spellbooks, which have no real-world equivalent? How do things like how the item affects that players stats (on servers with stats) factor into the scaling? Even when you can find a real-world equivalent, it doesn't protect you from having huge initial/"official" value vs. market value gaps because the supply of and demand for an item in the server's economy is probably going to be radically different from what it is in the real-world economy.

The second suggestion has very little to do with having a "successful" economy and has a whole lot to do with keeping players dependent on NPC shops. It seems to be centered around some kind of belief that players buying from shops is "good" and players buying from other players is "bad" (or at least, the system you're suggesting is one that would discourage players from buying items from other players.)

Overall, it isn't really a guide to having a successful economy, it's a guide to fighting inflation/deflation, which can be an important aspect of managing a server's economy but isn't the ultimate measure of success. The ultimate measure of success is the economy's ability to attract and keep players (for example, you wouldn't want to introduce some kind of anti-inflation measure if introducing it would cause you to lose more players or potential players than the inflation that would result from not introducing it would.)