Actually I talked to one of the guys who told me he bought in a store called Jeanus. If you look at the french authorised stores, this one is part of them. I even have bought my RMC there, and of course there is no doubt about its authenticity.
So we have different possibilities :
he lies and he didn't bought it for more than 700$ (500euros)

you guys are too suspicious about fakes lol

the store was scamed and sold fakes for the price of real RMCs

the store scamed on purpose the people who bought these Yoropiko and took advantage of the fact that they already sell real RMCs
I didn't see the jeans but I think the most likely is that he tried to lie to me, but we can't be sure