Thank you for your inquiry, the stores are sorted based on distance from nearest to furthest locations. You can set the distance radius setting at admin settings page, you can refer to this article here for better understanding.
If you’re using Show All as Default Map Setting, you can edit the sorting by editing ssf-wp-xml.php file. Search for keyword ORDER BY and you should be able to customize the sort based on column name, asacending, descending, etc. Take note MySQL knowledge is required in order to perform the code modification.