Interesting thought that's popped into my head since lemmy's population blew up.
These services are essentially individual sellers that all come together on a centralised platform provided by these sites to perform these services.
Aside from the logistics and distribution I see little reason why they can't be federated. Ebay could definitely be federated since individual sellers handle their own delivery, there is no ebay warehouse as far as I'm awar. Amazon on the other hand hold stock in warehouses making this considerably more difficult.
For taxis it would? I think. There's more complication in the ones with delivery. But the ones that are straight up 100% software problems like Uber can actually be replaced. I am actually thinking something similar to blockchain has a real viable purpose here (but not for currency/sales) because one problem you need to solve is reviews, and having the federation keep a ledger of reviews verified and maintained by everyone in the federation makes sense.
You'd still have the same issues that Amazon has about fake reviews. You would have to spend resources making sure the reviews for products/services are legitimate and not spam or paid reviews