I am not an expert, but lots of people do a lot of money buying and selling tibia coins.
I have not the patience to, so what I do, if I see that there is a realy good offer in my world or other world of an item, I usualy buy and transfer it to other world where this item is more expensive. This usualy works if you buy items from NA to European, because in european servers items are usualy more expensive; it also works for moving items from pvp servers to non-pvp.
Other think I have done when I move a character between worlds, is to buy 'cheap' stackeable items as gold tokens, silver raid tokens, dream matters, clusters, imbuing creature products, dishes, etc, that I can resell in the new world. This is how I normaly pay the 'transfer' of the real items I want to move from a world to another.