The reason why it's important not to rely on so-called "professional retouchers" instead of professional eCommerce photographers who are skilled in image editing, is multi-fold.
First and foremost, a "professional re-toucher" does not have an eye for photography, in most cases doesn't even see the product before retouching and therefore more often than not will make the image completely artificial and misleading to the consumer. Reliance on quality eCommerce product photographers highly skilled in image editing gives you the advantage, for the mere fact that when you have quality photography with quality cameras there's less retouching necessary. The editing is also far more precise because the professional eCommerce product photographer skilled in image editing, throughout the process, has the clearest idea of the final product in mind, and will in turn accelerate the entire operation as well as maintain the quality.
The only reason to go with a "professional retoucher" and not a professional eCommerce product photographer skilled in image editing, is if you want a massive amount of returns of your product from dissatisfied customers.