I wouldn't blame everything on BestChange, but I wrote about their terrible review system multiple times and I demanded improvement and update.
They don't update it because they don't want to. I know people who use Bestchange for years without knowing if there is only a green number showing good reviews it doesn't mean there aren't bad ones, you just don't see it. Many people believe if only the number of good reviews is shown so there aren't any other. The update of the review system isn't difficult to implement. It's a few database queries and can take 30 mins maximum to develop.
If exchange is using third party exchange they need to publicly show this and say they can freeze your coins at any time, otherwise I wouldn't use this exchange at all.
I think the same, exchangers must publicly show they use third party.
But even in this case an exchanger can't demand your personal data and can't freeze your coins. In this case an exchanger should give you contacts of that third party and that third party must be a legal company with an authority to check documents and freeze coins. I mean, anyway an exchanger can't freeze you funds by itself.