The simple answer is, have them sign an NDA (non-disclosure agreement). That protects your idea. But, again, if you can't afford to enforce it, then there's n

The simple answer is, have them sign an NDA (non-disclosure agreement). That protects your idea. But, again, if you can't afford to enforce it, then there's not a lot of point in doing the paperwork. And, many developers (and designers) won't sign NDAs just for discussions. In reality, most freelance developers have more work than they can handle, and pick and choose their projects, and aren't going to steal anyone's idea because then they have to program without getting paid, and it would ruin their professional reputation. But, if you can't afford to pay market rates to reputable developers, then you're looking for a co-founder to pay in equity or profit sharing. Again, now you're back to trust and respect. If your idea is so simple that a skilled but unscrupulous developer could go off and immediately clone it and make all the money you were going make, then your idea wasn't very original, and there will be lots of other competitors in the market in a few days anyway. Your goal, with doing all that research up front, before you ever talk to a developer, is to understand exactly how unique your app will be, and impress the developer that not only is the idea a good one, but working with you, with all your experience and knowledge, is the best way to develop it.