question What is the incentive for private sellers to report their sales to Namebio?

[DomDB]

Pretty much the title.

Why would a non-aftermarket seller take the time to report their sales to @NameBio when there is seemingly no benefit of doing so?

NameBio does not publicize the private seller (i.e. "Private"), so there is no marketing benefit or bragging rights.

 

[Kyle Tully]

Sharing data and giving back to the community, increasing comps for keywords or extensions, proof of stuff you’re already bragging about.

 

[DediRock]

Some sellers do it for transparency or to help the community gauge market value—even if it’s marked “Private.” It’s more about contributing than personal gain.