Then simply don't sell to them.
When someone is determined to do evil there's nothing a NICS or UPIN background checks 10 day waiting period private sale or Home built from scratch or 3D printed people have been doing evil things from day one either using firearms knives vehicles flammable liquids clubs stone's or good old poison even their bare hands and evil it's a unbiased with either gender or whatever you identify yourself in today's society in some of the most restrictive state's we have the strongest gun laws how's that working out for them the only one who benefits from this are criminals and the politicians who are in power disarmament of the law abiding citizens is what is intended look back in our history our own government has done more evil things I'm not talking about in other countries during war times or during conflict but on our own soil to our own population' evil dwells in all of us so our government will continue to add more and more laws and regulations and that mountain of God given rights we hold so dear is slowly being ground to dust especially when today's society is know longer chipping away they're using explosives and all of this just because we want the ability to defend ourselves and our families what a lovely world our kids will inherit 
Not when you're tired of all this BS we've been putting up !
