I found this site that provides this service https://bookcoinshop.com, but as I said on that topic, trust is the most important thing in designing those sites.
You need a powerful escrow service to ensure your site is honest, as well as handling all your requests will be impossible.

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I suggest the following:
Create an online selling site as localbitcoin, who have accounts [PayPal, Amazon] and others who have [Bitcoin and altcoins].
The site provides an escrow service until shipment and confirmation of the product, buyer release escrow.

So you are planning to give people aP dream come true then. Purchasing an item on a major online shop with a cryptocurrency is what crypto holders want. In this matter, we can now fully use the word "currency" on its name not only for an investment. A crypto mode of payment is a good idea and a chance to have more crypto users.

Sounds very interesting, would like to know how you plan to integrate with existing networks?

The question is actually this: are you able to compete with existing services that already do this.
Purse is pretty much exactly the sort of service you're describing, they're also pretty successful.

What stores did you have in mind, other than Amazon?

It's like a third party website that just connects you to the biggest and leading e-commerce websites. **Correct me if I'm wrong with this.

Is this what the diagram looks like.

Customer pays crypto ----> Cryptoshop uses PayPal or any payment method in $$ ---> Amazon and other not crypto accepting shop.