While this is common I still think this is wrong, I mean look at online casinos, they do not give loans to their customers and yet they are a thriving industry and it would not surprise me if they were generating now more profits than land based casinos, so trying to take advantage of gamblers in this way by giving them loans may work for a time and increase the profits of that casino, but I am sure there are many gamblers out there that if they found out this information they will decide to stop gambling at that casino out of fear this could happen to them.
online casinos will never provide loan facilities to their customers because that will be very risky because so many customers come from countries that prohibit gambling, so even if they provide credit card guarantees or KYC it is very risky for online casinos.
it's different from land-based casinos, in that the country or city certainly allows the gambling business, so it's only natural that land-based casinos provide loans to their customers. and I'm not sure if gamblers would avoid the casino if offered a betting loan because we know that not all gamblers are sane minds but many gamblers will accept such an offer.
In the case described in OP, the gambling agent was still able to find the gambler despite the gambler trying to evade the debt. If this were to be online casino, how and where will they find a gambler who they granted loan to. The money is lost for ever.
In general, I don't think offline casinos giving their customers loan to gamble is ethical. They are just increasing the gamblers debt and risk of being addicted. That act should be prohibited.
This only happens in the offline physical casino where the agents can trap the gamblers and force them to gamble even if they do not have the money. In online gambling, we do not face such a situation an online gambling site won't give loans to the gamblers. Yeah, they sometimes may give us extra money in terms of bonuses, etc but we can't withdraw that amount because of the high wagering requirement associated with those promotions.