Thank you all for your recent replies in agreement. Since my original post (last summer) I have NOT gotten any bug-infested bags of feed from this store. I continue to be professional & courteous when I go there. It's an independently owned & operated store, so there's no corporate office to complain to. There still aren't any other feed stores close enough to be competition. I haven't seen that staff member that was so rude to me, I may just keep missing him on his shifts, or maybe he turned into a bat and flew away.
I will continue to check my feed, especially during the summer months, and politely ask for an exchange or refund if I find bug infestations. It's good to know that I'm really not the only one who doesn't want to give bug-infested feed to my chickens.