Keys for a successful project:
Break off a piece of your application and work on building or improving that for a short time. Initially this should only be a few hours of work that both parties go over carefully before starting work on the next iteration. As you gain more trust, you can work in larger chunks, as long as communication is fluent. Regardless of trust, there should at least be some kind of demo and significant testing at least once per week. Note: do not start work on the next iteration until you have received payment for the previous one.
Attack Challenges Early
Identify technical or business challenges early on and try to address them right away. Prioritization is key. There is always a temptation to add many different features or ideas. Its critical to focus on the most important aspects of the system, and especially start to work on them early if they are difficult.
You may consider posting some information about payment in the project thread. That would include a reception of the code and working demo or iteration, an agreement for payment and amount, as well as the sending and receiving cryptocurrency address. This provides a public record of payment or non-payment which others can check. It could save someone from being scammed or taken advantage of in the future if there is a problem.