In all honesty, this will be a mixed bag, as the Google Shopping results generally are. There are also good price comparison and tracking sites now, but lots of us don't shop that way.
If you know the product and search for ABCbrand and 123model then the Shopping results are pretty good. As soon as your search is more vague the results are often very poor. As are the local results, as very few retailers are actually good at showing local stock levels for sku level deals etc.
This is also US only at present, plus Google have been trialling a full shop solution on US Google Shopping for some time, where you stay on Google and get it delivered through Google. Thankfully this has met with limited success. This is partly due to poor retailer data setup and shipping options being just too messy. But, it also partly relied on retailers going down the AMP route, which hasn't had great take up, as it only helped Google make money, to the detriment of individual retailers websites...
The reality is that as
@Mr D says, local, national and international retailers have to adapt quickly to survive. It's a similar situation that's been playing out since the start of online retail, or the advent of click and collect, eBay, Amazon etc. If you don't keep up and promote your business in the way customers are looking for products/services, then you will be left behind...
The complexity of needing a website feed, Google Merchant Centre setup and then setting up and running successful Google Shopping campaigns is beyond many small online retailers. It shouldn't be, as you can run efficient local campaigns very cost effectively, as even some large retailers don't do it well. It's all about product data and negative keywords, as with a bit of research and testing you can stop your products showing for irrelevant searches and only show up for real buying intent type queries.