You should be very wary. Once he is across the boarder with your machine, if he does not pay, it will be very expensive and difficult to collect from him: without getting into the particulars, there is no good mechanism for a U.S. citizen to sue and collect money from someone in a different country. That he won't provide  deposit is suspicious: it suggests that he may be intending to abscond with your machine, leaving you with no good pay to pursue him for the money. Of course, if no one else wants the machine and you'd otherwise be throwing it out, there may be no harm in taking a chance like this--but be aware that it is definitely taking a chance.