That mail in certificate policy is really dumb.
People are looking for convenience and value. I don't think Camping World offers either. The whole idea of online shopping is to find it easy, get a good price, order it easy and have it delivered quickly. If you have to physically mail in a coupon and then wait 6 weeks to see if your account was credited, I'm just not going to participate.
Camping World just sent me an email a few days ago announcing a huge discount on a Coleman LXE grill (not that I need one). The advert bragged about the big percentage discount on the grill, resulting in a price that I can beat by a large margin just by visiting any local big box store on any day.
I honestly do not know how these guys stay in business.
Being lied to like the OP was would seal the deal for me too. Yes, he was just one employee, but he certainly understood his sales mission to push for getting membership renewals, didn't he? You'd think he would understand how the program should work...or did he intentionally lie to seal the deal? Used car dealers have been doing that for 75 years.