It is possible to set the item location filter to "US only" and then lock that setting in the app. I am not sure if the lockable filters are enabled by default; you may have to go to your filter customization and turn that on. Once you do so, you should see a padlock icon next to some filter options. Set the option and then tap the padlock icon until it appears locked to lock that filter setting.
The "US only" item location filter selects items that are listed as being in the United States; however, as you may have seen, not every seller that lists items in the US ships from the US as they should. You can report such sellers for item location misrepresentation, but until eBay actually cracks down, your best course of action is to avoid such sellers entirely.
Before ordering you should check the estimated delivery dates -- that is usually a good indication of how far away items actually ship from. Also, going to a seller's profile page or feedback page will tell you where the seller's account was registered. Although some overseas sellers do use US warehouses to ship their items (and some US-registered sellers may employ overseas drop-shippers), if a seller is registered overseas, that raises the likelihood of an item shipping from outside the US, particularly for multiple quantity commodity items. Checking seller feedback will often reveal if there are problems with long shipping times, canceled orders or other supply chain warning signs.
When faced with a long list of search results that you want to narrow down to sellers that can ship quickly, using the "Guaranteed Delivery" filter will often help; very few sellers that ship from overseas qualify. That is a rough filter, though -- many domestic sellers may be filtered out as well.
