I do nothing.
I just sit there and listen to them, curse with them and let them blow as much steam as they need, you'd be surprised but most of the time people already know what to do, all they need is to be allowed to embrace whatever they are feeling at the time, to be heard and some empathy.
If you are afraid of an awkward silence then don't be, sometimes just sitting in silence with someone can go a long way. Sometimes just little questions about it can help them open and show that you care.
Not everyone wants help, not everything has a fix, not everything has to be fixed on the spot, forcing someone will only make them double-down or close themselves and that can get worse because they'll stop looking for help.
Obviously... this is in general what I used to do, everyone is different so each person requires a different approach,
I mean... It's not the first mexican government to do this and I doubt it will be the last (specially being so deep in with the narcos), usually ends up being the local seller's family giving the old guns away and getting some spare cash while the seller still buys more guns, so the cycle continues.
Sometimes weird things happen, like someone bringing in bazookas or a fucking torpedo.