Probably nobody cares about warranty on these as they are pretty cheap anyway, even if one or two are deffective, unless of course you get a whole batch of bad ones... but still not Ok to not even check them.

It is already somethign that you expect to happen when you buy risers directly from China, but with a local reseller that sells them at a premium you expect that they will at least do a check a couple of them from a batch they recieve before start shipping to customers. That is not happening either in most cases.