To allow the CDC to come into their country to help would be the same as saying "we are not capable of taking care of it ourselves". Its a sign of weakness and we wouldn't do any differently.. in fact, very few countries would do it unless they were part of some allied group, which China is not.
They have allowed the WHO to come in.
As for trusting them, most people don't even trust our own government, so that's not really a significant statement in that regard.
I said before, I'll say it again.. I think China is being as truthful as they can be.. That's not to say they are being accurate, but I don't think they're intentionally hiding anything for any conspiratorial reason. My guess is that they were overwhelmed and needed time to adjust the speed with which they started throwing resources at this.