Collecting minifigures - How, when and where to buy?

At first I started collecting lego sets, then I started collecting collectable minifigures. After that I was able to make a great deal in getting a lot of star wars minifigures (not that I am a huge star wars fan but the opportunity came along). Then I began collecting super heroes and other theme based minifigures. 

I find it difficult now that i have a rather large collection to complete my collection. I try to find them second hand to be affordable but then a lot of the tiimes they are not complete or just wrong. So i use bricklink a lot. But what i do not understand is how sellers have 50 or 100 unique minifigures only to be found in one set. You do need to buy a set to get the minifigures, but how in such a vast number? Are these fake or are there realy people buying 100 sets of lets say the green lantern just to sell the minifigures? 

I end up buying sets myself for the minifigs in it. But that is also rather expensive and takes a lot of storage space. 

Are there any minifigures collectors on this site/forum and how do you guys/girls collect the minifigures. Buying sets, bricklink, second hand, ebay, etc?

thanks