I've used many different bitcoin third-party shopping agents in the past, they've all vanished. Some company in Germany and a service called SnapCard (guess US based) that went under few years back.
This kind of service is occasionally being offered on many BTC or alt platforms, and somebody will sure use it, maybe offer your service through the marketplace at particl.io ?
If you have morelinks to any past and current services please let me know. I myself want more of these services in existence so it legitimizes the idea.
https://shopinbit.com/concierge-service-ordering-service is the best one that I know, but only for EU (plans to go worldwide soon).
Thanks for the link to particl.io I am checking it out.