These marketplaces already exist via DMPs and data brokers like Axciom, Neustar, etc.
There are cookie onboarding companies like LiveRamp, etc. that partner with companies and apps to load their cookie on login, map it to a hashed email, collect geo data, etc. and then resell that audience to these companies and advertisers to target/retarget against.
A surprising amount of that happens behind the scenes in apps where you'd have no reason to suspect they were doing that (the infamous "flashlight app requesting tons of permissions" is one example), and no real way of auditing it short of monitoring your traffic for calls to their servers.
I've heard rates around ~$8 CPM for each unique email-mapped user/mo (they pay you monthly even if it is the same user in Month 1 and Month 2 because the point is resetting the cookie that may have been previously wiped). Obviously various factors impact that pricing.
Adobe is also making big moves in that marketplace space for their Marketing Cloud [1].
There are cookie onboarding companies like LiveRamp, etc. that partner with companies and apps to load their cookie on login, map it to a hashed email, collect geo data, etc. and then resell that audience to these companies and advertisers to target/retarget against.
A surprising amount of that happens behind the scenes in apps where you'd have no reason to suspect they were doing that (the infamous "flashlight app requesting tons of permissions" is one example), and no real way of auditing it short of monitoring your traffic for calls to their servers.
I've heard rates around ~$8 CPM for each unique email-mapped user/mo (they pay you monthly even if it is the same user in Month 1 and Month 2 because the point is resetting the cookie that may have been previously wiped). Obviously various factors impact that pricing.
Adobe is also making big moves in that marketplace space for their Marketing Cloud [1].
[1] https://marketing.adobe.com/resources/help/en_US/aam/c_marke...