Users who are owed money (sold more than they bought) are not included in this list. I am assuming most clubs will want to pay these people in cash when they drop off their lots, or by check afterwards (address is required before submitting a lot, and is listed on the invoice). This will allow you to avoid the Paypal fees for these users.
I know. Ideally, I would integrate completely with something like Shopify or Paypal, and handle all payments seamlessly on this site.
Unfortunately, any payment method that allows credit card payments allows charge backs, which means a massive amount of paperwork and liability for this site.
And any payment method that doesn't allow charge backs (like Bitcoin) is very difficult for end users.
By using this feature, your club is taking on all the risks of online payments -- like charge backs and taxes. But, it's very handy to click a couple buttons and invoice all your users.
At the moment I am not aware of other payment processors that support batch invoicing from a CSV file. If there's one you'd like to use, let me know -- it's not difficult to export the data.