A guest wants a factura. Who issues it?

The sale is yours, so the factura is yours to issue, from your own SAT account. Rent La Ventana is a US company and can't issue a CFDI.

Most guests are from abroad and have no RFC. For them, use SAT's generic foreign RFC: XEXX010101000.

Once the booking is paid you have each other's WhatsApp, so ask them there for the details you need.