What about something with Amazon
Basically, people could buy anything from Amazon but within your site. Not sure how to implement the idea. Maybe using services like BitPay.
You could make a clone from Amazon website, people buy items (delivered by Amazon) and pay in cryptos. The coins are converted to fiat automatically (with Bitpay or any other) and your Amazon account is automatically topped up with a bank account (the one you used to receive BitPay payments)
I believe this has already been done in the past. I don't think you have to go as far as making a clone. Websites in the past just simply had a input where you could enter in the URL of the item, and it would open up a ticket for you to purchase the item on the customers behalf.
Be sure to have a large amount of funds available for early customers, unless you plan on converting the BTC to USD automatically, and making the purchase that way. You would have to profit off the spread.