In the letters I have so far received from some developers, they expressed their commitment to safeguard my personal data against their own abuse but I don't see any commitment that they will take responsibility if my personal data end up with other parties. Meaning, they won't be sending me promotional materials if I convey to them that I prefer not to receive any such materials from them. However, if other companies send me, then it's not their problem even if my contact details reach these 3rd parties through the developer.
I am saying this because every day I receive at least 2 or 3 sms or call and sometimes up to 20 calls a day from real estate agents asking me if I wanted to rent or sell my properties through them. How do I know they got my contacts through the developer? There was one day I went up to the developer office to fill up a form for my parking access. The developer asked me for another contact number and I gave them my mum's. That was the 1st and only ever time my mum's number has been given for any of my property transaction. That evening itself, and since then, my mum has been receiving calls and sms-es from estate agents.
I also found out from a friend who works for a developer that owners' list are commonly sold to marketing companies and estate agencies from RM500 and up to RM5,000. Some property owners I asked welcome calls from estate agencies especially because they can help them rent or sell their apartments. But that's their personal preference and they do not understand my pain since I have a few properties and sometimes getting hundreds of calls a week is not funny at all.