Here's what I'm doing in my campaign and so far it's kept player character power levels about balanced:
Restrict players to the Player Handbook, Rules Compendium and Miniatures Handbook ONLY. This applies to classes, feats, skills, spells (basically everything).
Disallow all forms of multi-classing; pick your class and when you level up in this class only.
Placed absolutely no magical shops into the campaign world.
The amount of money that shops and market stalls and merchants can offer for any magical item is a tiny fraction of what the magical item is worth.
I would recommend taking such steps in your own campaigns to keep things balanced.
Restrict players to the Player Handbook, Rules Compendium and Miniatures Handbook ONLY. This applies to classes, feats, skills, spells (basically everything).
Disallow all forms of multi-classing; pick your class and when you level up in this class only.
Placed absolutely no magical shops into the campaign world.
The amount of money that shops and market stalls and merchants can offer for any magical item is a tiny fraction of what the magical item is worth.
I would recommend taking such steps in your own campaigns to keep things balanced.