Should I pay upfront, and what is a reasonable percentage? — answered by Engineer Saeed Baatiah
Yes — a deposit is normal and justified, because the developer is reserving time they cannot sell to anyone else. A reasonable share is 25 to 40 percent. What is not reasonable is full payment upfront for work not yet started, or a deposit above half. Tie the deposit to an early deliverable — a design prototype or a first working version within two weeks — so you see a real signal of progress early instead of waiting until the end.