See this thread:
https://www.technofino.in/community...ard-application-via-call-whatsapp-mail.17470/
Basically these HDFC agents apply for your card using the offline method on behalf of you by printing these docs and sending offline applications to the HDFC Chennai branch in bulk (with their referral info) because this bank has such outdated procedures while other banks do Aadhar OTP validation and V KYC regardless of how you applied.
Unfortunately, for HDFC the only way to get the card of your choice or a LTF card using the card to card offer is the offline process if you do not see the card you want as pre approved or in the online application.
So, if you submit your docs, you will likely not be scammed, but you are giving up your info in a digital format. And for sure these agents will save your number and call you later for other bank's cards.
If you go through the offline method, it is just as shady and the agent can make photocopies of your printed docs and still add your number to their list. I don't think any of the agents even in the branches are full time employees of HDFC bank.
That's just the unfortunate reality of applying for HDFC. I got my card this way because firstly, I was not aware. Secondly, the overall security of this whole offline process is the same whether the agents prints the docs after you send them on whatsapp or clicks the pics of your docs on their phones once you leave the branch.
Sometimes there will be third party agents doing income verification sent by the bank after V KYC (so I could trust them a bit more) and even they asked for docs over whatsapp (not ID docs but ITR, which contains equally private info - axis sent that agent)