Since January 2nd, when the ban on private gun sales went into effect, it became much harder for Nevadans hard up for money to sell off their gun collections for cash. Private face-to-face sales were made illegal when universal background checks went into effect. Many of the first-time gun buyers panicking are responsible for this law as Clark County was the only county to vote for Question 1 in 2016, which emboldened the Democratic majority in state government to ram through SB 143 in 2019.
So no, you can't privately sell, transfer, or lend a gun to someone who isn't a relative, with very few exceptions (follow the flowchart and yes, we know it's confusing). The only time you can legally let someone use a gun for self-defense purposes is when the threat is imminent and as a soon as the threat is over. The law implies a scenario like an armed home invasion robbery of your house, not to a woman who is being threatened by her creepy ex (though there is room for debate).
If you want to sell, give, or let someone borrow a gun who doesn't meet the exemption criteria under the law, the gun must be transferred through a gun dealer (FFL). The problem with that is Carson City is so backlogged and overwhelmed with background checks, it is taking hours, days, and even a week for the check to be run. Even private gun sales/transfers to someone with CCW has to go through the dealer/background check process.
So no, you can't just sell or lend out a gun. It's not that simple anymore. Elections have consequences.
As for ammo, no restrictions on that. If you want to charge your neighbor $50 for a box of 9mm, that's up to you. Though you should be generous and toss in roll of toilet paper to cushion the blow.