Today we did a lot of driving. And we happened to go by a couple of farms which have started their own CSAs recently. I will not say which ones, because these are observations only.
One of these farms had a small (40x50 or so) garden in the side yard, surrounded by corn, soybeans, and hay. We drove past it a second time to see if we were missing anything behind the barns. It is hard to hide a garden for a mid-sized CSA. The small garden that was there were so many weeds you could barely see the rows. High yields are typically gained from "clean" gardens which do not compete for nutrients with weeds which are taller then the plants.
The second CSA had a small farm stand. We went in to see what they had. They had quite a bit... including plums with UPC codes. There were a couple small garden plots near the stand, but again not nearly as much space as you would need for a small CSA, yet alone a mid sized one PLUS a stand, which had 4 cars pull in during the 10 minutes we were there...
Now, I need to say that there are quite a few FANTASTIC CSAs in our area, with committed growers who are passionate about what they do. If you join a CSA look around! In general, one acre can support 20-40 members. So a 100 member CSA needs somewhere around 2-1/2 to 5 acres in production!!!! Not one small plot. If you see early June tomatoes you should also see a hoophouse (greenhouse.) And if you cannot grow it in your garden at that time you should ask yourself how can your farmer - often there is a reason they can, but not always.
CSA farmers NEVER stick UPC codes on their produce, and neither do most small farmers or even mid sized growers selling locally. A UPC sticker is usually a sign (at least in Ohio) of non-local produce.
I have said before and I will say again it is a buyer beware market and your best bet is to know your grower! We live in a region in which there is the ability for anyone to buy cheap produce at wholesale markets. Very little of this is grown in anything close to a sustainable manner.
It is my opinion that if you don't know your farmer you don't know if you belong to a CSA.