Creole, unfortunately the information DOES get shared from time to time, whether it was intentionally or not. There have been MSPs that have had their computers hacked, equipment stolen and equipment confiscated and sold at auction. There have been employees of MSPs or scheduling companies who have had privileged information that have left and taken that with them for whatever purposes. And there is little doubt in my mind, though absolutely no proof, that one outfit that collects shopper information is responsible either directly or indirectly for providing shopper contact information for scams.
In this day and age I don't see that there is much way of avoiding this kind of "sharing". We can only hope that companies will handle our information with care and confidentiality, yet when I contacted one about registration problems with their website and mentioned in passing being uncomfortable with putting a social security number on their unsecured website, their reaction was, "We've never had any problem with that." Of course THEY wouldn't, only the shopper who was compromised by an unsecure website would possibly have a problem.
Yet we DO need to provide the information to these potential employers if we intend to work.