My company would like to know if there is a legal form that a potential candidate can sign when we are paying for there flight and hotel and then they decide to not show and we are stuck with the bill.
The short answer is yes, you can.
I signed one for a company I interviewed with way back in the day. Its actually a reasonable thing to do from the companies perspective.
This will be dependent on local laws though, my experience is based in the USA. Speak to a lawyer for more specifics as to how to word the document.