So here is the thing. A membership allows people to sale things that they can not do legally otherwise. It would be nice if they offered a lighter level of membership for those who would use LESS than the normal amount. Maybe you could ask for that instead or simply say that your consumption is less than what they offer. I too am not able to use up as much as a membership would give. However, being a mature adult I do not try and force people to feel bad or guilty because I am not able to utilize the items they are offering for sale.
The Hammond family is working to make a living for their family by farming and providing the fruits of their labor and land for us to purchase. The membership program gives them a customer base from which to work. It doesn't sound like the program is workable for your lifestyle, but it isn't something to be disparaged in an open forum.
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I would guess a membership is like a pre order to ensure both that they grow the right amount and that you have opportunity to purchase. I know most just send a standard box at particular intervals for a monthly or weekly fee