Last year was the first year our pack sold popcorn at all. It was completely voluntary and maybe half the boys participated. Our previous CC didn't agree with turning our kids into little salesmen and refused to even consider it. He preferred to have one large fundraiser. The CM didn't like putting all our eggs on one basket and introduced the popcorn when the CC left.
School here starts the last week in August. Before the first week is over, the schools are handing out fundraiser sales packets for knick-knacks and overpriced candles. A week after those are turned in, the PTA is selling cheesecakes. Meanwhile the soccer teams are selling pizza kits and frozen cookie dough. After all those sales wind up, it's Girl scout cookies followed by Basketball season, and those kids are selling something, followed by the school's spring selling fundraiser and baseball/t-ball selling pizza again.
We bought some popcorn for ourselves, but didn't even try selling it to others, because we'd just hit everyone up with another fundraiser. This year, we know it's coming and we were surprised at the quality of it. So, I expect we'll sell more this year.
BUT both my husband and I are involved in the pack leadership and give of our time and money constantly. We wrote off over $1000 in scouting expenses/donations on our taxes last year. And that's all things we don't expect reimbursment for. Other things we are reimbursed for, but often have to sit on the receipts because someone forgot to balance the checkbook or some other accounting error.
So, all that said, I don't believe in minimums for popcorn sales. However, there are other options. One example is that any boy that sells over X amount has the profits from any remaining sales go to their expenses, be it membership fees or daycamp, or a uniform allowance or whatever the pack decides. One pack I heard of found this technique to be very successful and several boys had all their expenses paid for through popcorn sales.