The response? Lawyer up and threaten to sue.
NOTICE:Just FYI guys, it's 'libel', not 'slander' when written. Had you actually 'sought legal council' (that would be counsel btw), you would know that.
The SRAA has recently received a large increase in new visitors. While you are free to disagree with our message and site, you are not free to make slanderous and defamatory comments about us or our members. We have sought legal council and are aggressively and actively pursuing such individuals and groups that make such statements and will hold them liable for damages. If you have seen somebody making slanderous and defamatory comments about our group, either in person or on social media websites, please report them to firstname.lastname@example.org.
Update: And they're gone. Sorry 'regular guys', if you were just trying to sell some cheap ammo, you don't advertise yourselves as an 'alternative to the NRA' or any other advocacy group. You advertise as an 'alternative to high priced ammo dealers'. You also DON'T use Paypal nor an unsecured HTTP source for credit card orders.
Bye bye now.