When I was in Italy in the 80's, finding the used market of stuff was difficult.
But, all of that may have changed with websites like Craigslist, Facebook Marketplace, Ebay, etc.
Around here there are quite a few people who work out of their home. Buy, or are given good project bikes. Fix them up and resell. That takes away some of the needs to carry a big diverse inventory.
However, buying a few things in bulk may save a considerable amount of money. So you should be able to get tires, tubes, brakes, etc, at least at half the cost of new.
A unique market is stripping and shipping (Ebay).
If you can get popular big-name items for cheap in Italy, then it may pay to ship them to the USA or elsewhere. Think Colnago, Pinarello, Merckx, Campagnolo, etc. The higher quality the better.