There are situations where all ammunations are robbed/shot inside then you can't buy guns what can be really annoying. My idea is to add weapon dealers IG.
A player would go with his car to a specific location, buy specific guns and amount of them, and sell to other players. Guns would be cheaper in these specific locations, and every player would have the opportunity to add prices for each gun and bullets. Weapon dealers CANNOT use the guns they buy, because some would abuse this feature
If player A sells guns to player B, if there's a police officer near by, both will receive a 2-star wanted level. Police can take the guns to the PD and receive cash + score OR they can take the guns and use it in combat.
This could be a nice feature in game.
Feel free to modify this suggestion.