The process really comes down to who you deal with. Some people who have 1 positive feedback will want you to ship first however you do not have too. However if someone has a pretty large amount of feedback you should feel generally safe about shipping first.
Make sure to always:
Talk to the person and make sure the entire deal is laid out
KEEP ALL PMS AND COMMUNICATIONS
Person with 0/0/0 feedback- "You came to my thread so you with 75+/0/0 feedback ship first." Come on now -__-