Can anyone tell me “how effective your own gig videos are in ranking? even if the video is very ordinary?”
Does Gig Video Help in Ranking?
Fiverr is unlikely to release their data on this. You can judge the effectiveness of a video, however, by creating one, uploading it to your gig, and tracking interest to see if it brings in more traffic/sales for you. You are a businessman. Part of being in business is trying things and experimenting to see what works for you.
There is no single answer, and nothing works the same for everyone. Try some things, and see if you get the results you seek.