There is a risk for the Client and for the Coder. As I talked in another post that there are several Coder who tell you the blue from the sky and you could loose your Money, there are also Clients who think you work for free. 

This People let you work hours and hours and than they may decide they don’t need that product or don’t like their own ideas and don’t pay you.

When a Client pays you Money he is in Risk you are a good Coder, when you work for a Client without Money upfront you may find out you get nothing.

My best Experience is that

• I work usually on Advance Payment, also I often work around one up-to two Hours without payment to feel comfortable with the project. 
• Than when I understand how much work it will be I charge arond 50% Advance Payment. 
• After completing the Mainpoints 25% more
•  and when its done and the Client happy with the result, the rest 25%

I just can advice. Take your Time to feel Comfortable. It always depends on the relationship with your client and about the project itself. Be flexible and try to negioate that what you as a Coder and the Client feel comfortable. It does not make sense to work for or with someone if you always have this bad feeling in your stomach something could go wrong, usually than something will go wrong. That’s an advice for a Client and also for any Coder.

No good or cheap money is worth the headache you can have with a client who drives you crazy or a coder how does have more promises than experience.

Avoid to be stiff, be flexible. Within the first Project between a Client and a Coder you have to get the right feeling. When you have done some Projects together you both will know how it is the best to handle further Projects. When you are a Coder and need some Projects, invest a free Hour (and maybe get the Job, instead playing around for nothing with your own Ideas). If you are a Client and like to motive the Coder give him a small Budget with what he can show his Talent.