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 really good offer in my world or other world of an item, I usually buy and transfer it to other world where this item is more expensive. This usually works if you buy items from NA to European, because in european servers items are usually 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' stackable 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 normally pay the 'transfer' of the real items I want to move from a world to another.