1. No there is currently no pricing model which allows for funds to be charged only after an item is sold. The actual transaction for sales of items listed does not take place via ClassiPress, as the buyer and seller do this themselves. The only payment process is that which happens when a customer posts an ad on the site.
2. The only percentage based pricing model is" % of sellers ad price" which is based on whatever they're selling their item at, but this must be paid before the ad is published, not after sale.
3. Again no, as the actual sale process does not take place within the website.
4. We do not currently have any ecommerce based themes. If you were to use ClassiPress, the customer can of course reduce the price of their items by editing the price.
5. You could customize the ClassiPress theme to prevent contact in this way, but the whole purpose of the contact form is to allow the transaction to take place between the buyer and seller.
6. This is not built into the theme, no.
7. Some people have been able to customize the theme to work alongside a rating plugin, but again, this takes customization.
Basically everything you have described does not fit any of our existing themes, although ClassiPress is the closest which is why I am responding based on that theme. Based on the fact you have described that you have no computer/website skills, I would not recommend this as your purchase unless you were planning to invest money into
hiring a developer who would implement any such changes for you, as none of these are included in the out-of-the-box theme. Although even then I don't think this is what you're looking for.