I hire developers from time to time. I avoid the situation you are currently experiencing by asking for a development plan which includes milestones and a requirement for "reasonably" documented source code. After agreeing on a price, the fee is split based on the milestones, and paid as code is checked-in and the milestones are reached. If the developer doesn't meet the schedule or decides to bail on the project, then another developer can pick up where the previous "coder" left off.