Need help setting up a weekend "bake sale" like event please

First, I'd make sure you were using the table correctly. Drag items from your Sim's inventory to the table. Click the table, select "Tend table." You may also need to click "Stock table" to make the merchandise appear. Once you've got your Sim tending a stocked table, click the table again and select "Start yard sale." That last step is what actually prompts customers to come and shop your stuff. It will be a timed event you can repeat as many times as you want.