Factual error: At the beginning Scrooge is seen signing Jacob Marley's death certificate in the year 1836. English Birth, Marriage & Death certificates didn't come into being until 1837.
Continuity mistake: In the scene when Scrooge is talking to the boy after he changed, the boy has a sled that was right by some posts, but after Scrooge gets excited because he didn't miss anything and we go back to the boy, his sled is now further away.
Revealing mistake: During the scene when Scrooge is sitting in his armchair by the fire, the animation of the fire is badly looped and you can see it flickering as it finishes a cycle.
Continuity mistake: While in Scrooge's office, the businessman on the right is about to write down Scrooge's contribution in the ledger, with his pen close to the page. The next shot shows the businessman's writing hand and pen away from the ledger.
Answer: Mr. Scrooge is a moneylender and Bob is his clerk. Moneylendering is different than something like a bank loan because interest rates are much steeper and usually the last resort for poor people who can't get bank loans. In essence he's a loan shark.
Bishop73