Its possible some think you can do something nefarious with the RID before you buy it, but that's a stretch.
If they were really D* employees, they would know that could not happen.
There are a few members on here I'd feel ok buying from without asking for the RID but generally a moot point as they'd likely put it in the for sale posting anyway.
That's a problem.
You will now find valid owned RID numbers on various sites advertising "owned" units. These valid RID "owned" numbers have been harvested from ebay, craigslist or other sellers - perhaps here? The sites even give the Access Card Department info to call and verify. A sucker calls and Access Card Department says "yes, its owned" because it is owned - just not by the seller.
Sucker end up with nothing or a leased unit with a different RID and a big hassle on your hands.
Has not happened to me, but I have found many websites that has the RID of one of my owned HR34s. One website when you click to buy goes to Amazon.com where you end up purchasing a leased unit (the Amazon site never says it is owned).
So you go to the website, gives the RID number (mine), you verify, Access Card Department says "owned", you click to buy, you are on Amazon.com website. You purchase. You've just been scammed - but would you have expected it?
I would suggest no RID numbers on ebay or craigslist or here - only give them to someone who private messages. And if buyer, ask for a photo of the RID on the unit or screen - not just the number itself in an email.
Furthermore, when you call the Access Card Department for verification, HAVE THEM NOTE ON YOUR ACCOUNT the unit is owned at that time. If you do not, I had one situation where they tried to say a unit was not owned when I finally activated it. Took a while to straighten out. Would not have happened if they noted it the first time on my account.
EDIT: You may be interested in knowing I have called the Access Card Department twice about one of my owned HR34s RID being on so many scam websites. Told them they should note that so if anyone called about status, they could warn. Both times I was told they were not interested in doing so. So much for customer support.