I don't know how it works on Google Shopping, but I do know that on vanilla Google, if two listings are identical Google will only show one of them. The others get buried in a line called "see similar listings" (or words to that effect). This can also happen if two listings are not absolutely identical, and not even from the same seller, but contain the same lengthy description. My son has an online drop-shipping store and I've spent a lot of time rewording descriptions supplied by the manufacturers in order to get his pages out of the pack.