Selling small is the best way.
Once, I managed to pick up a 9 bar of resin from out of town for £120, and sold it for £5 an eighth. There was a huge drought on at the time
where I live, so nobody cared. £240 profit, thank you very much. Lots of chopping and weighing though, and so much time spent waiting for people to come round to pick up. My first and last foray into the world of dealing, and I can never be arsed to do it again. Unless I find a huge ass bag of weed somewhere, and even then I'd probably just smoke it all.