Crowley had tried to let the man make his own bids, really he had. But if some of his own temptation just so happened to seep over to the other, well... it wasn't like he was trying!
The man was only a couple thousand dollars in the hole, although Crowley would be interested to see how he chose to settle his debts.
"Perhaps you'd like something to eat, Doctor? Assuming you feel you can afford it," Did Watson have any scope of the money he was losing? Of course, if they ended up having to 'work something out'.