I belong to a fabric co-op (so we can buy thousands of yards at a time to keep costs low). If ONE person backs out- then the price is raised for the rest of us. So we have a "Strike" rule to prevent this. You get one 'give me' strike (for running into money problems/or unexpected family troubles) and then the second one you are on probation with the group (no buying for a period of time). After that, once their full membership is reinstated again, if they do it again, then they are completely kicked off the group and NEVER let back on again. It works and it's enough to scare people into being very serious about what they are buying and paying on time. There should probably be some kind of system like that here. Maybe not exactly like this one, but something along those lines.