Hi David,
It looks you have not properly uninstalled the extension in your store.
Please follow the below steps in your site.
1. Uninstall the extension in your store.
2. Then delete the below tables in your DB.
sales_flat_quote,
Delete field seller_total_shipping_amount
sales_flat_quote_item,
Delete filed sellerid,optionid,shipping_calculated_method,shipping_calculated_amount
sales_flat_order_item,
Delete field sellerid,optionid,shipping_calculated_method,shipping_calculated_amount
sales_flat_order_grid,
Delete field site_purchase_order_status
sales_flat_invoice_item
Delete filed sellerid,optionid,shipping_calculated_method,shipping_calculated_amount
Marketplace tables and setup in core_resource table
3. Disable cache and install the extension again.
If you still face the same issue, please email to support@modulebazaar.com
Thanks,