I'm not sure I believe them

I shop at Costco frequently. By that I mean at least once a week. Sometimes twice a week. OK, probably more like three. I do have a family of six after all. I don't buy big, extravagant items. I just buy regular grocery stuff. I have the regular kind of membership. The kind that costs $50 annually. Well, around 2 months ago my family and I were shopping on a Saturday. We were checking out and one of the associates came by with a hand held scanner and
pre-scanned our items before we got to the register. She then asked me if I was interested in upgrading my membership to the business type. With a business membership, you receive cash back rewards and that's about it. Nothing fancy. You need to spend $2000 annually in order to get the cash back. I told her no thanks, I looked into it when I renewed back in November and was told I had only spent $1200 for the previous year. (Their year is from renewal date to renewal date. Not the calendar year.) I was told upgrading most likely would not be worth it unless I planned on buying some big ticket items. She said, "well, it looks like so far this year you've spent....$1800. You're well on track to reaching $2000." WTH! (I, of course mean heck there.)
This was around the beginning of March. No way had I spent $1800 in three months time. Especially since I had only spent $1200 the previous year. I asked her to recheck and sure enough, $1800 was the amount spent. I told her I'd have to think about the upgrade and walked away shaking my head. No way could it be possible.

Well, back on the greatest day of my life, I decided to look into it again. This time I went to customer service and asked them to tell me my total. They told me my total spent was...$2200. If I upgraded I would get the cost of the upgrade back and then around $60 more. I was absolutely flabbergasted. I asked them to double and triple check the numbers. Really, I spent $2200 dollars since November 30, 2008 up until then. (It's actually a little higher than that now because I've been back a couple of times since.) In five months time, I've spent more than $1000 dollars more than I did the entire previous year. I just don't know how it's even possible. Like I said, I just buy regular grocery stuff. Milk, eggs, cheese, string cheese, cottage cheese, sour cream, orange juice, chicken, other meats, fruit snacks, laundry soap, fabric softener, dryer sheets, soups, crackers, chips, spices, granola bars, etc. Huh. When you type it out like that, the list gets really long. Maybe I have spent that much money....I'm still not sure I believe them.