The simple answer is, it's in the contract. Your contract with your developer, which you both negotiate and sign, says that you pay for them to develop your ap

The simple answer is, it's in the contract. Your contract with your developer, which you both negotiate and sign, says that you pay for them to develop your app, and perhaps would have a non-compete clause to prevent them from self-publishing a similar app within, say, a year. If they violate the terms of the contract, your lawyer sues them. Now, this is tricky in general, because app store submission processes are developer-oriented, and there will inevitably be bugs, which your developer will have to fix. There are a lot of details to hammer out on how to arrange all of that. But it's not a trust issue, it's just a paperwork one, as long as you can afford to enforce it. Now, if you can't afford to enforce it, then you do need trust. And one way to have that trust is to have respect. A developer will respect you more if you bring something tangible to the table. That is, more than just an idea. This is the long answer. If all you have is an idea, then a developer (or designer, for that matter) is going to have to figure out a lot on their own. They're going to have to figure out what you mean, who the users are going to be, what the users want, how the marketing will promote the app, what it should cost, how many users at one time the app will have to handle, on and on, every detail. There will be so many details that you haven't thought of yet, that the developer will have to figure out, that it will basically be the developer's app. Any developer (or designer) worth their salt is going to ask for at least 51% equity in your company to build your idea, because they will basically be doing all the work. The only way to retain control, and to earn enough respect to deserve it, is to do all of that work up front, yourself. That's the role of the businessperson in a startup. You do all the market research to figure out that people will definitely buy this kind app. You do all customer development to figure out what problem this app will solve for them. You do all the user research to figure out exactly how the app will solve that problem. You do the competitive analysis to figure out the price and positioning of your app relative to other solutions in the market. You do all the sales channel development to figure out how to tell people about the app. You do all the projections to figure out how much money you might make. And then you put that all in a Powerpoint to convince a developer that "all" they need to do is build it, they can focus on code and not have to worry about all that business stuff, you've got it covered. That's your job. An idea isn't good enough. There's a lot more than just programming that goes into an app, and you have to have covered everything else if all you want is a programmer to build you something. Good luck!