Hi,
The user selection is using the "namebox" system.
That system allow to perform search (on various fields, like "username" or "email") and it also have a dynamic loading (where you are at the bottom of the list, the rest is retrieved using an ajax call).
In the backend view "vendormarket / form" you will find the code which use the namebox type to display the selection of a user.
It is possible to add options in order to change some elements (like the sort) but there is no group filter available for the moment.
To implement new options it requires to modify the HikaMarket user class (which is core file).
Displaying only the users in a specific group is possible, it needs to add a filter in the function "getNameboxData".
$sqlJoins = array();
$sqlFilters = array('juser.block = 0');
if(!empty($options['filters'])) {
foreach($options['filters'] as $filter) {
}
}
With the variable sqlJoins you can add tables in the SQL query (to include the joomla user groups) and with the variable sqlFilters you can add the filter to only get the user in one specific group.
Regards,