To stop coin farming, brand-new players can trade with other players once they are 3 days old and level 5. Until then they can play normally, buy from the shops and do the "Trade 50 coins for 1 water" quest step, but they can't buy or sell with other players, send packages, transfer coins, pay stud fees, pay another player's arena or post paid jobs.

This only affects players made from today on. If you have played for a while, nothing changes for you.