validating/rejecting translation

are there any rules experts could/should/do follow when deciding to reject a translation or ask it to be edited?

It seems arbitrary at the moment.
Ive seen really bad translations given the chance to be corrected by the translator and other translations, with only minor defects rejected out of hand.

There are some here : experts task, but it's not really complete. We have to improve this field.

ok thanx. i guess at the end, the important thing is there a common set of loosely defined principles that are somewhat spontaneously applied by experts with peer review correcting if need be.
I'm not an expert but i asked because it's perhaps even more important for translators