This was when I was in college, bear with me.
Let's say 5 people want an 1/8. I go collect money from 5 people, 45bucks each. Now I have $225. I buy an oz for $200, and give out the 5 1/8s to those customers. Now I have $25 and 3/8 for free, for maybe 30min of walking.
So now I sell my other 3/8 at 45 a piece and now I have $160 in my pocket that I didn't have an hour ago, and I started with no money.
Middle man doesn't produce or consume, he transfers and is compensated for it.
I made a lotta money in college that way. And the best part is, I started with absolutely nothing but a bunch of people too lazy to get their own weed. Each of those people thought I was only picking up their 1/8th for them, not making money and free weed off of them.
But I was also taking all the risks of having stuff on me and transferring it from dealer to me and then from me to them. Risk vs reward.