H,
if there are more items sold from one address (same coordinates for more items), map displays only one of them.. Is there any way how to fix this and display all items on a map?

@Peter123
Can you show me such situation?

Yes, please follow url below:

http://shopsbook.com/search

test1, test2 and test3 have exactly identical location. In admin area I can see that they have identical coordinates, but as ou can see on map in frontend (search page), only one of them is displayed.

@Peter123
I can see that plugin is showing just 1 listing, not 3 of them.
Are you sure all of them has set same coordinates in database?

Yes, you are right, only one of three is shown.
Coordinates are all same. Please see attached image.

@Peter123
In oc-content/plugins/rad_search/listings_map.php
There is condition to avoid duplicates:
        if(!in_array($detail['latitude'] . '-' . $detail['longitude'], $already)) {
change it to
        if(!in_array($detail['latitude'] . '-' . $detail['longitude'], $already) || 1==1) {
to show all listings