They’d legally still on the hook for the difference, and if it’s a large enough amount for the creditor to care about they’ll come after you for it using the variety of means available. In the US that can include taking the money from the debtor’s bank account or having their employer take it out of their paycheck before paying the debtor.

There are some ways around that. You can self-employ and ignore the garnishment request, but that works best if you have a constantly changing client list, like a roofing contractor or wedding-dress-maker or whatever. You have to be careful about keeping cash in your business because they can show up with the sheriff and take any cash, or in extreme cases they can seize non-exempt property (like, they wouldn’t generally be able to seize the lawnmower you use for your lawnmowing business).

Also, just not having any money is a pretty good defense. There are limits to wage garnishment for example.

But yeah, in a lot of cases it’s not even close to being worth the effort to chase someone down to collect, so you get a ding on your credit report for a few years, and then almost nobody cares.