It depends. . .
As others have said, you don't want to sell to or trade with someone who might use the guns/ammo against you.
In general, regardless of what your trading, it's best if people don't know here you live. This applies to guns, ammo, gold, water, food, medicine, slave girls. . whatever
That said, let me present some scenarios. I will not push one over another since I don't know what the future can hold.
- Total collapse of civilization (super volcano, plague, EMP.): Deep cuts in population. The classic Mad Max situation. Guns might be very plentiful in N. America, but ammo could be the real value.
- Fast Economic collapse: Crime will go up and odds are the government will become more controlling in response to the crisis, as the government doesn't want to lose control of the country/state/county.
Expect greater gun and ammo control. Mandatory registration of guns. ammo, owners, and tight controls of new sales, possibly leading to bans of certain weapons and ammo. Here ammo again would be of value, and so might guns. But you could be force to trade in the illegal markets which adds risk.
- Slow economic unraveling: Frog in the pot scenario. Guns and ammo still available, but every year the restrictions become more obnoxious, along with ever increasing bans on "evil" guns, magazines, and "cop killing" ammo. (think England), In this situation your guns and ammo could easily lose value as it becomes more dangerous to possess restricted weapons.
- No SHTF: Some guns go up in price and some guns go down in price. Guns and ammo are readily available.
Which will happen?
Make your choice and live with the consequences. .