Bidorbuy sellers don't always deliver

I have ordered a number of items from various suppliers listed on Bidorbuy and in most cases paid via BobBucks from Bidorbuy. I have not received so.e of the items after weeks or in some cases months want by and i have sent messages to the sellers with no reply. I'm starting to wonder how the pre screening of sellers are done as the one person from Bidorbuy said to me that they don't take responsibility for the sellers mistakes.