Tests for a Genuine Rudraksha.
To meet the ever increasing demand of different faceted beads, traders have started manufacturing rarely faceted beads such as the one faced Rudraksha body (The Ek Mukhi Rudraksha). Beads of Areca nut, Nutmeg or Tulsi are used to fashion Rudraksha Beads. In such circumstances the individual who wants to buy a genuine Rudraksha is in a dilemma

There are few methods of testing a genuine Rudraksha:
Cut Test:
A fool proof method is to cut the Rudraksha bead horizontally. One will find the same number of compartments as that of the number of lines . However the drawback is that by this method, the bead gets destroyed.

Properties Test:
The other is to find out whether the beads exhibit properties like inductance, capacitance, conduction of electric current etc.

The copper coin test:
It is generally held that if Rudraksha beads are placed between two copper coins it should rotate slightly. This is due to the physical and magnetic properties of the Rudraksha beads. This test requires a high level of expertise.

Eye test:
A fake or the artificial Rudraksha may look like a real one but in these Rudraksha the facets (mukhis) can not be made as real as those present on the real Rudraksha. In a Rudraksha the facets or the mukhis means deep lining from the upper part to the lower part of Rudraksha. Looking at these deep linings (facets) with the help of a magnifying glass, one can easily recognize a real Rudraksha.

Water test:
Some times a higher valued Rudraksha (Gaurishankar Rudraksha or a Trijuti) are made by artificially joining two or three Rudraksha with the help of glue etc. In case of doubt such Rudraksha should be boiled in water for one to two hours. A sharp discoloration will take place at the joint in case of artificial Rudraksha.

The test wherein the Rudraksha Bead dips in water (commonly known as water test) is not dependable because:

A fake Rudraksha made out of wood and impregnated with lead will sink in
water thereby giving a false impression of a real Rudraksha.

Some times a rare available Rudraksha (like one mukhi) is made by tempering
other easily available real Rudraksha beads of lesser value. Such
Rudraksha will also sink in water .

Still it is one of the most popular methods to test the beads and many times gives accurate results.

Source :
One of the best way to get a real Rudraksha is to source it from a reputed dealer