From my experience, no warehouseman will want to accept anything without documents, even CMR for transport. Such functionality is a quick way to make a mess in the warehouse. In the case of RMA, how do we know if this product has been sold from us? If you want to return something, first we call the seller and check if it is possible, and we do not send it immediately and later it will be there somehow. If someone did not take the goods at all and immediately returns - we have sales documents and we withdraw a specific sales order (RMA for the entire SO). What will happen if someone signs these documents that he has accepted something and should not? In the case of PO, how should we accept something that we could not order at all? Someone will say: "You have signed that you have received it, now pay". I do not see it in WMS. In addition, such goods must always be stored separately for clarification. We do not know who to invoice.
Such a thing can be done on a flat warehouse/stock (without WMS) and off balance sheet.