I know that there are proces that are set in stone pretty well (1 diamond 100rc for example), but I believe that one of the admins should create an info board either in-game or on the website displaying normal prices for certain goods. This way, if there is any large deviation from the original price, the seller (most likely ripping off a newbie) can be warned or banned. This suggestion is for those who do not know prices and are taken advantage of (I was one of them, a long time ago)
Comment on what you think

In MineRealms economy, it is necessary that the prices fluctuate, depending on supply and demand.

If set prices were enforced, the whole glowstone thing wouldn't work at all.

Trading is your own responsibility. If you trade without knowing the prices and get ripped off as a result it's your fault.

In general I am strongly against idiots being protected from their own mistakes, how will they ever learn if they are ever protected?

But can someone give us an tip how you can tell the prices on items then

By being in game and reading whenever a trade takes place

As others have said, there really aren't "normal prices." Supply/demand and all that.
No. If one player makes an offer, and another accepts it, then it's a valid trade. If you want to buy diamonds for 25 rc each, you likely won't find a seller... but if you do find one, congratulations. If you try selling dirt for 1,000 credits per stack, then don't expect many customers... but if you do find some, congratulations.

Wasn't there some stone slab buildings in 3.0 with the "ideal prices" on signs? I believe they were positioned on the intelli's tower realm.

No. This is (almost) a completely free economy and needs to remain so.

Not that I recall. Wasn't Intelli's tower a newish structure in 4.0 anyway? There might have been something of the sort in one of the private realms near spawn, back when shops were allowed in spawn realms.

Those "suggested prices" were the prices on the boards set by one of the shops by spawn. The reason why a lot of people used them was because they were conveniently reached with /spawn when you wanted to reference them.

Also, there is pretty close to no chance that any official, or even semi-official prices will be set by staff.