ebay doesn't have a shipping default and doesn't set the rates or decide where you ship to although there are a few countries they regularly block such as Russia. The exception is if the seller is using ebay international shipping (EIS) (which I see that on at least one of your ended listings) then ebay determines where that item can be shipped to. You ship somewhere using EIS if ebay will not ship that item there.
In your current listings, one ships just to the US. The other one ships worldwide but has quite a few exclusions including South East Asia. That's why Taiwan is excluded. Other than the few exclusions that ebay automatically puts in, if you are shipping directly and not using ebay shipping, the other places that you ship to is entirely up to you You can set up those exclusions in the shipping policies that you set up or if you are not using business policies, you can set up the countries that you will not ship to on your shipping preferences page. https://www.ebay.com/ship/prf
You can also set up or change country exclusions on the listing page when you do a listing if you aren't using business policies. You might want to change that on your two current listings.
Your listings state that the shipping isn't accurate but it should be as your shipping cost is strictly based on the information that you put it in the listing. If you use flat rate shipping you need to figure out a shipping cost ahead of time based on the service and the country that it is being sent to. You cannot adjust the cost once the item has been purchased. The shipping needs to be correct when it is listed.
It's more accurate to use calculated shipping. You can enter the package dimensions and weight and the service or services that you want to use. Then the buyer will be charged shipping based on their zip code or their country. The only time I have seen a problem with the usps calculator is if the wrong information is entered. UPS and Fedex can have some upcharges that might not be calculated at the time of purchse so if you use the calculator for those services, you may pay extra after the item has been shipped.
