Understand there are difference in prices between a brick & mortar Boutique and the internet/online eshops, which is extremely tempting
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I'm not sure if the pieces are new or pre-owned. From what you mentioned, the online shops provide the warranty. It is of no use if the warranty is not back by the manufacturers. Should any incident happens, I doubt you've any recourse. Furthermore, there are some replicas or counterfeits around.
I would prefer to have the peace of mind getting from either the Chopard Boutiques or their Authorised Distributors.
Happy Hunting... please let us know when you've purchased the MM.
Kong