How do I reply to a quote request and turn it into an order?

This needs the Request for Quote plugin. Quotes are under Orders → Quote Requests. Click Settings there to choose who sees the button (all or selected products), guest access, a Min quantity and the Button label.

1. Click Open on a request. Reply in Conversation; the customer sees the thread under My Quotes in their account.
2. In Respond, fill in the Subtotal, Tax, Shipping and Discount fields. WCart works out the Final price for you. Optionally set Valid until and a status such as responded or accepted. Click Save.
3. When the buyer agrees, click Convert to Order.

WCart creates a Pending order with the quote's items, address and agreed prices, so its total matches the quote. The quote is marked converted, with a link to the order. No payment is taken at that point, so collect payment and update the order's status yourself.