Yes, each member account has a balance without any restrictions in either direction, and it mostly works fine. At times, the negative balances pile up, in which case I write a mail to the mailing list asking people to pay their dues. Usually, the negative balances approximately cancel out the positive balances, both at something like 1000 euros.
Also, when your balance is negative, after every purchase there is a big red notification reminding you of that.
Also, when your balance is negative, after every purchase there is a big red notification reminding you of that.