There's escrow services, but they cost money, and he won't be able to access/use it until you give the release saying the job has been completed. There'd be nothing stopping him from just keeping that money and bolting at that point. Unfortunately there's no 100% perfect way to avoid being scammed in this situation. Ask for screen shots, demo's of the bot working, maybe even teamview with him if possible. Try and outline a schedule, whereby he'll deliver screen shots of his progress, or even better let you teamview with him. Maybe every 2-3 days you guys can get on team viewer together and he can show you the progress, and as it gets closer to being finished he can show you a demo of it working.
There's no guarantee's there either, but usually someone wouldn't agree, and then comply with everything along the way, only to rip you off at the very end. That doesn't mean it won't happen, there's plenty of scumbags on here, but short of standing over their shoulder it might be your best bet. Do your homework on whoever you decide to work with though, google their name, skype name, anything you have, and see if anything phishy comes up. Good luck though.