Have a look at chrono24 a monitor how long the watches are on the site for.
The general rule is the higher the price the longer the time it takes to sell so you need a large holding fund
To have a stock to sell
Have a look at the window at your local jewelry store
Compare the sites on the net they are you opposition
An make sure you know how to spot a fake ....... becase in the high end your buyer has that experience or the contacts to get it