how much u pay as deposite depends on your negotiation with the PG but always make sure u had B&W. Most of the time, 60-70% of the sum should be paid after you get back the photo and that you are satisfactory of the works.
Also, try to to look for a reliable photographer, always check that they are ACRA registered company (ask for their company registery number) and a B&W contract signed by both parties. You can check on ACRA website for registered company :
http://www.acra.gov.sg
Business profile can also be obtained at $5.
Personally, I had a terrible experience with our PG that we paid deposit to him (a freelancer), but he MIA with no photo returned to us.
When we tried other contact means to get help from CASE or Subordinate courts, it won 't work, cos they are not registered.
Unless it is a very reliable source and word of mouth from a very close contact, do not engage any freelancer. it is not an isolated case on my end as there are quite a lot of cases from freelancing companies already. if you are interested, we discuss on this thread:
http://www.singaporebrides.com/forumboard/messages/7/1317514.html?1270977682