Well, usually, the grower makes up for it by adding more vegetables from the bumper crop. So if you can't add a tomato because it's been a rough tomato season, you might add two or three peppers instead. There's generally a lot of good will between the grower and the buyers. It's smart of you to ask about the pitfalls though. One thing to remember is that you aren't likely to make a substantial amount by fulfilling your CSA obligations. The trick is to include add-ons that will appeal to your new customers. They can order those extras as they desire and that's where a good portion of your profit will come from.