There are built in costs to members' noncompliance to their commitments -- and noncompliance is usually a result of inability to overcome domestic opposition, not strategic willfulness on the part of the national authority responsible for foreign policy. The penalties for non-compliance come in the form of "allowing" affected member governments to impose trade sanctions of their own on imports from states that have been determined, through by an elaborate, multinational decision and appeal process, of being in violation of their commitments. Even then, states impose sanctions only if the they can muster sufficient domestic support for them - there is no automatic sanctions coming from the WTO as such, so this isn't in any way a level playing field among countries. Such sanctions serve as a domestic political weapon to help encourage pro-trade factions to prevail in domestic policy contests by encouraging exporters to also support policies which liberalize competing imports.
There is, therefore, nothing at all deterministic about WTO agreements. Rather it just provides some political tools that may, or may not, help pro-trade coalitions within nation-states prevail over anti-trade coalitions. Stronger international institutional arrangements such as NAFTA or the EU provide somewhat better weapons for domestic the pro-trade factions, but even then the outcomes are far from unambiguous.
On China's (current and/or future) ability to make use of WTO agreements and regulations to force more international compliance (even by the EU and USA), are you equally skeptical? The march of civilizations is a series of defenses that man has put up against the dread of pure existence.
