> There used to be 3rd parties defending consumers by testing products back in the days

And what happened to them? Why did they go away?

It wasn't due to the government outlawing them.

> The problem with government being involved is that this opens the door for easy corruption

And 3rd party reviewers aren't easily corrupted? There are at least some mechanisms to address government corruption in a democracy (elections). What mechanism can be employed against a 3rd party reviewer that simply lies about a product it's reviewing?

That's the reason this has to be government ran. Corruption happens regardless of who's doing it, government at very least faces some accountability.