David Pardue from Engadget tested the A7SIII and concluded:
I can’t find many faults with this camera. Sony has addressed nearly every complaint I’ve ever had about previous A7-series cameras, but it didn’t just stop there. It also improved autofocus and other features that I already liked, keeping the A7S III far ahead of rivals.
Its limitations are down to the high $3,500 price tag and low-resolution sensor, which rules out the A7S III for landscape and other types of high-detail photography. If you need that, get Sony’s similarly priced A7R IV with a category-leading 61 megapixels.
If budget is an issue and you need an all around hybrid camera, check out the Canon R6, Panasonic S5 or Sony’s own A7 III, all between $2,000 and $2,500. However, if you’re into video or low-light photography and have the budget, I’d highly recommend the A7S III. Feature for feature, it’s simply the best camera I’ve ever tested.