heres what u do:
Guide in steps.
In this method they trade you 2.5m worth
You will need 50k fire runes (500k cash).
Other person will need 50 *Uncut* Dstones (2.5m cash).
Step 1:
You sell fire runes in tzarhh rune store for 1 tokkul each,
this makes you a total of 50k tokkul.
Step 2:
Other person sells 25 *Uncut* Dstones to the gem store.
You buy them and bank.
Step 3:
Repeat step 2.
You have made 2mil cash out of this.
Dragonstones recieved = 2.5m
Fire runes used = 500k
Total profit = 2m
Other person comes out with nothing
That is how you trade between accounts.