Great question. I think you'll find that most video production companies are "reputable" however the bigger question is what kind of quality do you want and what is your budget? Having been a creative and video director for 20 years, I've seen budgets from $1,000 to $100,000 for videos, for widely varying types of projects. For a simple explainer you are looking in the realm of $500-$5000 depending the on quality and customization. There are places that charge more and do amazing work but those companies are typically creating work for bigger brands. Hope that helps.
There are a few options:
1. You can do it yourself — record your screen while you do the demo, toss the video into iMovie and add a voice over / captions on the screen for guidance. Benefit is it's fast and free. Con is it will likely be low quality..
2. Go cheap — you can use a site like fiverr.com for a cheap option. You can spend a bit more and outsource on ODesk. Benefit is low cost, con is quality won't be too great.
3. Go big — hire an video agency, develop a story / script, proper film production. Benefit is the quality, con is the cost (though you can likely find decent options for around $1k, but the good companies will charge >$5k)
In the end of the day, it all comes down to what your budget is, what your goals are with the video, and ultimately, who your customer is (if you're a consumer facing product, high production value goes a long way in my opinion).
Happy to chat a bit more if you need some more in depth insight. Good luck dude!