How a lot of "online" transactions work is that they complete the work, give you a demo (screen shots etc) and then you pay, and the code is sent.
If you need a hacker possibly someone more trustworthy can help (like me

) but you may wish to protect yourself just as much as the coder wants to protect themselves.
There are two sides unfortunatly, either the buyer gets ripped off or the seller does, so by providing, say a 25% downpayment with the rest on completion works quite well