You said there are some lines someone should not cross, no matter how desperate they are. Do you know what being desperate means?
When you are desperate for something, there is nothing that you can't do at that point in time in order for you to feed that desire or whatever arose from that desperacy in you, so saying there are lines someone should not cross when they are desperate is, in my opinion, impossible.
The person should not even get addicted to gambling in the first place because once they get addicted, it's hard for them to control what they can do and what they can't do.
Impossible? No! Nothing is actually impossible but sometimes we see things as impossible due to our weakness. Every gambler is desperate to win but then some of us do that with caution and play responsibly knowing that being desperate for win will not make us to win. For others, they think desperation would make them force the win to their ways while they play without applying wisdom.
Indiscipline gives birth to desperation which eventually lead to excess addiction. You can be addicted and still be using your brain to know the limit or lines not to cross especially with someone's else money in your possession. Some addicts are just partially foolish and using addiction as excuse for their foolishness.