Regarding the Allow sellers to require price extras feature, if it is enabled and you have specified Required opposite price extras in the listing settings, as shown in the screenshot Awesome Screenshot, then the customer will not have the right to choose the price of extras and will be forced to pay for this service, as you can see in the screenshot Awesome Screenshot
Do you know hot can I allow sellers to create a ctustom offer? Lets say the price 100$ and someone is asking for a special request and they want to do it sending a “custom request” so they can put the value there.
I tried few plugin but without success. If you want I can open another topic on “development” section.
If you have the Requests extension, users can post custom requests and vendors can reply with offers (you can also allow bidding), also you can enable private requests (users can send those via the vendor profile pages). If you mean sending an offer without posting a request unfortunately there’s no such feature yet.