Have you tried to do the math? Putting stacks of 5 for 250c each. That is 50 listings at 250c equals 12,500cr. That's 12,500cr!!!! Just search the GTN for Electrum, for example, on average it sells for 800-1200cr per unit but there is always at times some listed for under 500cr. Buy up all those and re list stacks of 20-28 for lets say 900cr per unit. That is 14k profit on average per listing. Multiply this by 50 and you make a minimum of 700k profit. This is just one material I'm speakign of.
I make plenty of money on my own without buying up other people's stuff to resell it. At least my way it's affordable to the people that need it and the gougers are buying it up too. So I have more demand