Here is my idea:
Blizzard implements a loan feature into the bank. The higher level you are, the more gold you can get loaned, starting at lvl 10. If the person doesn't repay the bank, they lose whatever they bought. The gold is tracked as well (like beside your money amount there is like 'Loaned G: (amount of loaned gold you have)') It would get rid of beggars, right?