Definitely contact the seller via eBay and explain your concerns. The issues with serial numbers don't really concern me, BUT the damage to the friction areas does. The issues with the balance pad area are not significant, either, as long as the weights are the same, so find a digital postal scale (even at your local post office, during off-peak times) and check and record each one.
Packaging? Put more protection around each one? Were these pistons loose in one box, with a cardboard divider or packed in individually-sealed boxes? Some "warehouse wear" from contact with the cardboard during shipping might be acceptable, BUT not the nicks and such. Other than basic clean-up, they should be "ready to install" when received. In this case, "not useable" for many.
These pistons are probably "rebuilder pack", if they came in one box, rather than "retail pack", which would have been individually packaged, I suspect. That's why the price was probably less than other sellers? As such, they were not really meant to be shipped "cross country" but delivered from their distributor's warehouse to the machine shop. HOPEFULLY INSURANCE WAS PURCHASED as one of the first things the seller can claim is that if it was "shipping damage", then "it's not their deal", but the shipper's deal.
The broken factory seal might be a moot point unless the seller inspected the items prior to shipping them. But if that is the case, then a notation should have been made on the box of such an inspection prior to shipping, it seems. In one respect, a good seller should inspect what is being shipped out, but that could also depend upon the orientation of the people doing the shipping themselves AND if they might know what they are looking at.
Good luck!
CBODY67