Omega - where to buy preowned?

[Calla-lilies]

Hi there,

I am going to buy an Omega De Ville Prestige watch for myself - just because : )

Hope someone can provide some guidance.

I am open to buying a preowned watch if it is authentic and that's where it gets a little hard. There are many eBay sellers but I don't know enough to tease out the faux pieces. Are sellers from Japan more reliable? since they usually do not sell counterfeits? (Or am I wrong here)?) Are there reliable sellers?

Also, I see that Jomashop offers them at a lower price point than Omega -- I've been trying to educate myself on the grey market but I'm not entirely sure if I understand -- I think grey markets also sell authentic pieces?

Thanks!