Adding a shopping feature to your website, akin to an Oxwall store but tailored for selling items like cars, clothes, and more sounds like an exciting endeavor! Integrating a system where members can list their products for sale, akin to eBay, and even compensate owners for their services adds a layer of depth to the platform. 

To implement this, you'd need a robust e-commerce solution with customizable features. For instance, setting up a variable VAT for different product categories based on search tags is a sophisticated feature that would require careful planning and development. 

Moreover, enabling guest purchases through popular payment gateways like PayPal can indeed attract more traffic and facilitate seamless transactions. 

Considering the complexity of your requirements, it might be beneficial to consult with a web developer or utilize a platform that offers customizable e-commerce solutions. With the right tools and strategies, your website can evolve into a dynamic omvormer of online commerce.