One other thought: weigh your ingredients when you get them home. I started doing that after one batch seemed about a pound off. You can always adjust quantity based on what the weight of ingredients are. I think it's just a case of the LHBS being a little casual depending on who is working there, since the weight is likely to be a little off in either direction, whether it's hops, grains, or DME.
As noted in an earlier post, I also watch the LHBS folks like a hawk, but I still weigh when I get home. My hops were actually well over the 1-ounce measure per packet last time.