Many Performers will bring merchandise to sell at the show. 100% of merchandise sales should go to the Performer - it is not appropriate to assume a cut as a Host. Please offer a small table or counter space for displaying their merch (often this will be determined by how much merch they have to display). Most Performers bring their own float, pricing signs, inventory sheets, and keep track of their own sales. Please have a discussion with the Performer before the doors open about how they would like merch to be managed for the night. It may be possible for the door person to help keep track of sales. Some artists will have a merch sheet listing how much each piece costs and allows to count off how many were sold, which typically the merch person fills out at the start and end of each night. If you are really keen, you may even consider having a float on hand (just spare bills to make change with). The best way to help is to just ask!
Please remember - it is NOT appropriate to take a cut of the merch revenue. Side Door does not condone this, unless it is something the Performer agrees to.