An alternate model would be to make search good enough let consumers find stores within a radius of their current location selling X, and price compare them. E.g. I need a widget - stores a, b and c are selling it. Store a is $14.99 and 5 miles away, store b is $8.99 and 15 miles away, store c is $11.99 and 20 miles away.
1. Dig something out of your basement that might be worth something; Treadmill, Pokemon Cards, etc.
2. "List" it on Google Shopping
3. USPS picks it up and delivers it
4. PROFIT!Just search on shopping.google.com and then in the filters on the left side check the box for "Available nearby".
To achieve convenience requires either building out a logistics infrastructure on the scale of Amazon, which is clearly a business Google doesn't want to be in, or to approach the problem from the opposite direction. Brick and mortar retail is declining, especially post-pandemic (but also pre); that said, there is already an infrastructure that exists transfers goods to retail locations - it's just spread over 10,000 companies rather than 1. However, if you can write software to better utilize that infrastructure so that you allow consumers to find items that are already physically close to them, and ship using either "last mile" crowdsourcing (and eventually auto-driving vehicles), or at least direct consumers to where the items are so that they can travel less than 30 minutes and get _the_ item they want, then you can come up with a credible anti-Amazon alliance.
Example: I want to buy a sun shade for a pergola. There are probably 10 stores within 20 miles of me that carry them, but I have no idea ahead of time the brands, the price, the color, the size, etc. I could spend an hour calling the stores, and have irritated minimum wage cashiers do inventory searches for me an attempt to answer my questions. Alternately I can go on Amazon, make a purchase, and have it shipped in 2 days from a warehouse 900 miles away from me.
Having something shipped from Amazon, and other non-local webshops means waiting for a few days, or weeks. While ordering from any online store (even the mom and pop retailers) within the country will almost always be next day delivery, and you get to pick between at least two shipping companies.
For selection and availability, pick any local price comparison site, and just order from which ever is cheapest and have the item in stock.
Whenever you want to set up a shop and sell over internet, you would reach out to a shipping company and arrange a pickup time for your orders. The company truck visits every day at a specified time, then pick up that days orders for shipping.