Assuming that five different websites would all run a re-targeting campaign for the same lamp - it's tricky, and you would probably be relying on the retargeting cookie expiring, or you hitting the frequency cap for each.

It's possible that at the level of the ad network the products could be disambiguated, and then cancelled so that other companies did not waste ad spend. This would be difficult as the products would have different SKUs.

At the level of a single retailer, the retailer places a burn pixel on the checkout page which registers to no longer place ads for that product.