Check the buyer/seller feedback section. There are a lot of "I hate Z1" threads. And there are a lot of "I Love Z1" threads.
It's all about tact. If you have a legitimate problem with a vendor and can word a post with enough details to substantiate your problem, there should be no reason to delete it.
However, if you just make a thread that says "Z1 sucks my nuts and so and so can blow me", chances are really good that it will get deleted.