Well....all I can say is that Malcer Angalstrand made his first fortune by buying magical plate mail and skill buff items on TLR and then hiking to WD where he would sell it for a huge profit to wealthy DF PCs who lots of gold but less access to that particular equipment.
I didn't have formal DM "buy in", but I'm pretty sure they all knew what was going on and the team always seemed to find a way to rid him of his gold through IC purchases of housing or exorbitantly expensive alignment masking or scy-blocking magics needed to keep his arse alive.
The concept worked well (both for generation of income for a PC that couldn't solo 3 goblins and as good cover story calling him a "Waukeenar" merchant) and it definately took advantage of inter-server variability in buyback rates, merchant inventories, a player wealth levels.
Could it have been viewed as exploitive by a DM...certainly. But *shrugs* it never seemed to be a big issue to me. Maybe I just had understanding DMs or such.
One thing I did do however was RP investing in storage facilities along the road, shops, carts and horses etc. None of them existed in game, but just throwing away a few trade bars and then calling it done seemed good enough for the TLR team. (until I actually got my tabacco shop built...which was really cool

)