Welcome to the forums
While there are a few sellers that I would be more than happy to deal with you still need to be careful, don't assume just because they sell on here everything will be fine.
I know many here will disagree but for me, if you're even slightly what your looking for regarding authenticity and who to purchase from go to an Authorized Dealer. Yes you lose out on potential savings but the peace of mind would more than make up for it.
Good luck
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In 1953 they used Rolex Oysters and oxygen on Everest.
In 1978 they managed without the oxygen.
Rolex Explorer -- Rolex Datejust -- Tudor North Flag -- Omega De Ville Trésor -- Tudor Black Bay GMT -- Omega Speedmaster Professional -- Tudor Black Bay Fifty Eight