Answer 1

Well, first, there is 10% chance pickup will activate after battle
Also, you get better things the higher level you are

Lv. 21-30
0.3%

Lv. 31-40
0.5%

Lv. 41-100
1%

http://bulbapedia.bulbagarden.net/wiki/Pickup_(Ability)

Comments

thanks kagmin7

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Tip
Dont try to get good items with pickup
U need to use multiple pickup pokemon with high level at once
(That are too weak to be trained easily)
And it is pain in the ass from experience