Sellers who are dropshipping often have no idea of how many items their supplier has in stock.
They often have never seen the items they are offering, until someone decides it is unsatisfactory and returns it to the seller.
The item is often warehoused and shipped from overseas, which can cause customs problems.
In this case, the seller was caught out.
You should expect a prompt return of your entire payment. You have up to 60 days to leave feedback. The most effective feedback is calm and factual. "Poor inventory management. Listed items not available." for example. When you leave fb you will also be asked to leave Detailed Seller Ratings which are more important than fb.
The lowest Rating is ONE star. Sellers whose DSRs drop below 4.3 find their ability to list and sell is restricted or removed.