Thank you so much for your interest in our Revo theme and contacting us.
1. About the vendor, there will be option for you to approve a vendor in your site in the vendor plugin settings if you use WC Vendors or WC MarketPlace plugin.
If you use Dokan, you can enable the user to create an account as a normal user. After that, you can enable them to be a vendor in the User Settings.
2. For auction plugin with vendors, you can try plugins that are recommended by the vendor plugins as below:
If there is any difficulty during using our theme, you can contact us at our Support System then our supporter will help you.