I was playing around with the buy/sell technique and found a much more efficient way of doing it.
Start with roughly 13000gp (easily done with a few quests) and head to Bowerstone North. The merchant there that sells black roses should have 40+ diamonds for sale at approximately 250-270gp per. When I went he had 49 diamonds for 265gp each.
I followed the potion idea, and in the time it took me to count to 30, I made over 100,000gp. If you took 10 minutes to trade potions back and forth, what might happen in 10 minutes of diamond trading?
It is fast enough that I have decided to see if your allowable coin maxes at 999,999.
