Why does eBay allow multiple Sellers to sell the same object under 3 diff #s?

[onebadwolf]

This exact same watch is listed by 3 different sellers, under 3 different eBay item numbers.

antique-yokohama-jp                 #143898245847

https://www.ebay.ca/itm/Casio-Marlin-W-550-Digital-Vintage-Mens-wl19619/143898245847

tomimu64                                      #154226305714

https://www.ebay.ca/itm/CASIO-W-550-81-Watch-with-swordfish-top-Vintage-working-product-Digital-rare...

Oriental-Vintage-Modern           # 124412420109

https://www.ebay.ca/itm/VERY-GOOD-Rare-Casio-W-550-Mens-Watch-From-Japan-EXPEDITED-SHIPPING/12441242...

What if 3 people buy the same item?

[marnotom!]

At least two of them will get ripped off if they're not careful.