6) No FFLs
Here in Canada, if someone in BC wants to sell a firearm to someone in Alberta, or someone in Ontario wants to sell to someone in Saskatchewan they can do so as long as the person they are selling to has a valid license that allows to them to possess and acquire the class of firearm being sold.
However, in the United States if someone wants to sell any firearms to an out-of-state buyer (such as a person in Texas selling to a buyer in Arizona) can only be legally sold through a Federal Firearms Licensee, or FFL for short. The FFL would act as a middle-man (and charge the middle-man fees) to transport to the buyer and finalize the transaction. FFLs are also required for the transaction of NFA-regulated firearms such as SBRs and fully-automatic firearms, however they are not required for sales of non-NFA-regulated firearms between two private individuals within the same State.