IE Amazon can pass the buck completely to the sellers.
This will simultaneously make it expensive for those sellers actually trying to comply (lab testing is not cheap), and do nothing for those that were likely the problem in the first place (who will just fake lab results and do so at a lesser price)[1]
They should require amazon to randomly sample.
[1] In case you think this is not a real problem note that similar kinds of lab testing requirements destroyed, for example, children's toys except from large scale sellers who could afford the cost of compliance (see https://www.cpsc.gov/Business--Manufacturing/Business-Educat...). You will find basically no small manufacturers of childrens toys anymore. Different cause, but likely same effect.
I'm sure it made things safer in some sense, but yeah.