They either obtain from an authorized dealers or the manufacturer themselves.

They sell all fake products. There is a whole of difference in quality.

Yes, the service is as promised. Anyone can buy product from JomaShop with fair price

Because your company got a good deal from the other watch companies plus your customer services are awesome, there is more watches to choose than other.

I believe most of the watches sold by Jomashop are what are known as "grey market.
They are 100% authentic but can be excess stock obtained from an authorized dealer or sometimes even from the manufacturer themselves.   Often they are new old stock.    
Basically merchandise sold outside of the 1st level distribution chain.   Perfectly legit and quite common.

Because most of them are fake