Great questions!
1) It really depends on the data broker and the state you live in, but the majority are the latter (prevent the info from being displayed online). When possible we request full deletion, but California residents are really the only ones that have firm data deletion rights from the CCPA and are typically the only ones that data deletion is even made available as an option by the data brokers. We have some new product features in development that will increase our ability to deliver data deletions though in the future.
Regarding “If the latter, then this is only half a solution because the data broker can still sell your information”: this too is inconsistent. In most cases they will stop selling your information after the opt out, but in some cases, though they take the profile down from the public web, but may still be selling the data behind the scenes, usually to corporate buyers.
When the data is represented as deleted by the data broker, we don’t have a good way to confirm that it has actually been deleted unfortunately. We have some ideas though for how to do this in the future.
2) We recommend only submitting the minimum amount of information necessary to complete the opt out, which in most cases is the minimum amount of information required to sign up for Optery (first name, last name, year of birth, current city, current state), or sometimes also the URL where your profile was found. Many data brokers request a phone number to verify, but we recommend never providing them with your real phone number. Most of the time, demanding the data broker remove the profile and threatening legal action or reporting them to the FTC and your state attorney general's office over email will induce them to remove the profile without a phone number. If data brokers push back on this, we recommend you definitely file a complaint with the FTC and your state attorney general (we do this frequently). If you do feel you want to provide a phone number, we recommend creating a temporary, secondary, or disposable phone number. If you do opt outs on your own, we also recommend you always use a temporary or secondary email address for the submissions, and NEVER use your primary email address. We have a post on our Help Desk about this here:
https://help.optery.com/en/article/do-not-share-your-persona...
3) Definitely there are some data sets that are inherently difficult or nearly impossible to remove, e.g. public records, voter records, etc. However, we can often get this type of data removed from the for-profit web sites that re-publish it. The best best thing you can do is submit the opt out request. Some will honor it, and some will not. It’s hit or miss. The silver lining is that most of the web sites that re-publish public records usually publish more limited information as opposed to other sites that post things like phone number, email address, ethnicity, household income, network, family members' names, etc.