The link has to be from your item listing to a page on another website, that page also has to have a link to your listing.
i studied this years ago ..when i had a few yahoo groups and wonted them at the top of the google search,
one of them was a group for a small yacht called a foxcub ,it that was built from 1970 ish to 1982 ish.
So i posted links in the links section of my groups to all the top yachting websites who promised to return the link ..by having a link to my group in their links section.
it worked very well , i got my little yacht group recognised ...there where only 400 of them made, and somehow i got 500 plus members, the designer , the builder, was going well until yahoo closed all its sites ..by that time i had had enough - 20 years.
videos work very well on you tube. so if you video an item put it on you tube with a link .......that will improve its viability a lot.
my video is still there . but the group has gone.
https://www.youtube.com/watch?v=-dBx9u-Qh-o
all the best...mark