Irregularity in pu-erh
The best bet is to buy from a vendor you trust. And if you feel the quality is not correct to the point that it is “packed with dead weight”, I would notify them.
Most vendors should be familiar enough with their teas that they know the quality, but for some vendors who provide a huge selection of teas that they are reselling, that may not be the case.
Maybe taking photographs would be helpful, since it might be a case of a few bad sessions. I know of some cakes that have that “dead weight” syndrome, but they are not that prevalent. You probably won’t run in to this problem very often. At least I hope not!