Yes, there is a trick:
1- Call the Jiny
2- Drop the lamp before the Jiny is done talking
3- Select the person who will receive the wish (I think this must be done before the Jiny is done talking)
4- Get your wish
5- Pick up lamp
6- Start over from 1
Personally I was never able to get more than 6 wishes. But I know some people have got many more than that.
As far as the best wishes:
Power--->Arm of Argus
Weapon--->Sword of Argus
Those 2 are probably the best.
+50 HP, +1 to all Stats (max 24), Armor of Argus are preatty good too.
Good luck and tell us how many wishes you got
