Professional retouchers, just like artists, know exactly where a shadow should go and how the light should fall. They understand the human anatomy and are very familiar with the rules of composition and perspectives. A professional retoucher knows exactly what to emphasize and what to hide to make a photo look as good and as natural as possible. 

Professional retouchers have many techniques at their disposal - on average, most retouchers know at least 10 different ways just to retouch skin. Each technique has its own advantages and disadvantages - one might be suitable for one photo, and another for another. With all of these possible effects, techniques and combinations of the two, it takes an experienced professional to know which combination of techniques to apply for the best result. 

It takes years of study and practice to become a professional retoucher. If you need to retouch 10 photos, sure, you could try to figure out how to do it yourself, then practice, learn and experiment. Or you could turn to a professional who knows exactly what they’re doing and will do it much faster. You wouldn’t try to repair your gearbox yourself, would you? 

Sure, the cost of getting 10 photos retouched will be higher than the cost of a subscription to a do-it-yourself app, but what about the results? Getting your photos professionally retouched will make them look like a million bucks!