If some ads are sent (on Telegram) with the "sponsored" prefix shouldn't they all be? If some ads are categorized under "advertisements" on DDMS, shouldn't they all be?
No.
(Disclaimer: I have no idea about how sponsored deals work on DD.)
I don't believe all ads are equal. When I'm pushing my random no-name product from Amazon, and I reach out to DD to advertise, they need to let everyone know that they aren't standing behind this product or the "deal" and it's just an ad. However, when there's a good deal and someone from DD reaches out to the merchant to try to make some money off it it, whether by referral links or stickied posts, the deal stands on its own and all that's required is a small disclaimer that DD is making money. My $.02.