I've read that Lucasfilm used to be rather draconian in their pre-release approval process (but my understanding is thay was the exception rather than the rule). It's possible that if Eaglemoss released a bunch of crap CBS might pull the license, but my guess is the quality of the customer service probably means more to CBS than the products themselves.
That being said, to date, the only error that I think is particularly glaring is the backwards decal on Defiant, but even that is so relatively minor that I don't think it's that big of a strike on the overall line (and in no way would raise the ire of CBS). Other problems like the occasional crooked part or paint inconsistencies are to be expected on a mass-produced item a $20 price point. If it was expected that every unit would be picture perfect, it could likely raise the price just enough that the product would likely not be as viable.