I do not sell jewelry, but have talked to a lot of folks who do.
I had one couple tell me that they used a metal door under a table cloth for their magnetic jewelry (it helped keep it separated).
Another couple told me that they hooked their more expensive pieces down with a safety pin to twart would-be thieves (they caught quite a few).
The best thing I ever saw was a frame that was standing upright so the jewelry was hanging and very visable...but most importantly, it was clamped to the table (using clamps like you would in a wood shop) so that the wind could not blow it over.
A friend of mine lost a lot of glass jewelry in a wind storm. I felt very badly for her.
Good luck!