It's been a while since I've used sort by average customer review. Only useful sorts are "featured" or possibly price if you put in some filter parameters on the side. Anything else is just asking for hot garbage.
There are few things that I buy from amazon now that aren't shipped and sold by amazon. I just don't trust third party sellers unless it's a 'direct' seller aka the company making the product. Almost would prefer if amazon would just remove all third party sellers but I guess they need to maintain their reputation of being the everything store.
This depends on the item. Items that just use a UPC do get comingled, products that use an Amazon-specific barcode like an X00 do not, and this is required for some types of products (eg food or anything with an expiration date)
As I understand it, anything used or returned will also get an LPN barcode, which tracks that specific unit.
There are few things that I buy from amazon now that aren't shipped and sold by amazon. I just don't trust third party sellers unless it's a 'direct' seller aka the company making the product. Almost would prefer if amazon would just remove all third party sellers but I guess they need to maintain their reputation of being the everything store.