You can exclude shipping to locations that are in the list of excluded shipping locations - that's it.
If they are not island countries that are in the list, next best option is to exclude the countries that they belong to.
https://www.ebay.com/ship/prf/excludeRegionsAnother possibility would be international shipping rate tables and setting a prohibitively high cost on those locations if the tables are granular enough and you CAN even specify those island locations there (looks like same locations as exclusions list so maybe pointless) Has a drawback of not being an absolute block, and many others are reporting that rate tables are broken and not working (my domestic ones work fine)
https://www.ebay.com/ship/rt/?client=MyEbayI'm not even going to go into what an island destination has to do with increased refund frequency.