If I don't misunderstand the agent/casino and the bettors, the basic problem is credit from the agent to the user, because he only has 1k balance, because of the kindness of the agent, because he is a regular customer, of course the agent trusts 8k capital to bet, hoping that the user can win more than 8k, but damn he loses it all.
For that, if asked who was at fault, for me of course the user was wrong, he was greedy and didn't consider the risk of loss, he didn't think about taking 8k funds with what he paid for it, profit if you win and if you lose the bet as it has happened, of course the risk must be borne by the user to pay the credit funds.
The agent is not wrong, because he trusts the user as a regular customer, of course he gives the credit, it's still fortunate that the agent employed the user for several days to pay off the credit, that person worked without a salary, because the debt had been cut off.
From what I understand, the agent didn't gave 8k at one go but he gave small amounts first. The agent didn't hope for the bettor to win but what he only want is for the customer to pay on the designated dates. I don't think the gambler don't consider the risk of losing because he just lost earlier but indeed he was greedy. At that time, he is only thinking for a revenge but unfortunately, it didn't end up well.
The agent is only doing a business here or a kind of side job by letting the customers take a loan and the bettor in the story is only just a victim. None of them can be blamed but it would be inappropriate if the gambler will ran away for his obligations.