They should be rinsed daily. You'll want them in a container large enough to keep them in a layer no more than 1/4" thick. This generally means a sandwich size tupperware container for 1/4 pound, a shoebox size container for a pound.
Once daily fill the container with cold tap water, no need to dechlor. Wait a minute for them to settle to the bottom, pour off as much water as possible, they need access to air as much as water. The biggest problems I see is from people keeping them in too much water, not rinsing daily, or not refrigerating them.
If you don't want to refrigerate them you can keep about 1/4 pound in a 10 gallon tank, no heater needed. Run a sponge filter, you will have to keep the filter off the bottom as they will sneak into the pores of the foam.
To get a visual on it, here's a quick tutorial on another site;
Organic Blackworms - Blackworm Care
As far as the auction, my biggest downfall is the giant pizza slices. We hold our events at a park district facility, and have the gymnastic team do concessions, brings in money for their team. They bring in stacks of boxes of pizzas, I'm a real sucker for it, after a couple working the auction slows down for me.